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Engine Tune and Performance; Symptoms: FAQ Home
Volvo Maintenance FAQ for 7xx/9xx/90 Cars Version 7.2
Abbreviations
Note: Symptoms may involve several potential failures, so diagnosis should start with a general perusal of this entire section. Most of these notes apply to Bosch LH 2.2 and LH2.4-equipped cars. Regina-equipped cars have some differences in components and component failure patterns. Where known, these are noted in the relevent section. Diesel symptoms are covered in the diesel engine section of the FAQ. Some notes relate to carburetted cars: they are identified as such.
General Symptoms and B2XX Series Engines:
Idle Problems:
Poor Performance, Idle Surge and Hunt: Dirty Throttle Body Poor Idle;
TB Cleaned; Now Idle is Too High
Poor idle, Smoke, Oil Leaks: Clogged Flame Trap
Fuel Intake Carbon Removal
Engine Dies After Starting, Won't Idle; Needs Intake Cleaning
Poor Idle: Injectors Need Cleaning
Poor Cold Idle: ECU E-Prom Needs Update
Idle Speed Control Problems
Start or Stall Problems:
No Start; Frequent Stall or Hesitation: Basic Diagnostics
No or Slow Hot Start: Problem Diagnosis and Repair Guide
Intermittent No Start or No Warm Restart: Radio Suppression, FI Relay, RPM Sensor
Intermittent No Start: Fuse Contact Failure
Intermittent No Start: Washer Fluid Line Leaking Onto Distributor
Intermittent No Start: Battery Cable Connector Failure
No Start; Tear in Air Duct Intake Hose
Frequent Stall or Hesitation: Carburetted Engines
No Start, Poor Fuel Economy: Timing Problems
Stalls in Heavy Rain: Water Leak in Hood
Mixture, Misfire or Idle Control Problems:
Runs Rich; Black Smoke; Poor Acceleration: ECT, TPS, FI.
760T Floods and Stalls: ECT?
Cold Start, Dies; Dirty or Faulty IAC
Intermittent Stalling: Faulty IAC or Hall Sensor
Slight Hesitation on Acceleration; Several Diagnostic Checks
Hesitation; Poor Driveability: Bad Air Mass Meter Symptoms
Hot/Cold Air Box Thermostat and AMM Failure
Misfire and Broken Distributor Wires
Misfire Under Load: Ignition Power Stage
Stumble, Stall, Poor MPG: Bad Engine Ground Connection
Symptoms Related to Engine Sensors or ECU:
Engine Failure/No Start: Bad ECU
Hesitation, Poor Idle: ECU Failure with Codes 2-3-1; 2-3-2
Loss of Power; Rough Running; Knocking: Bad Engine Knock Sensor
Retarded Timing or Knock Sensor Code: Wiring Interference
Rough Running; Cylinder Diagnosis
Hunting Idle; Faulty TPS or ECT
High Idle at Startup: TPS Failure
Idle Surge, High Idle, Poor Idle: Vacuum Leak
Slight Backfiring While Coasting; TPS Mis-adjusted
Symptoms Related to Electrical Malfunctions:
Sudden Cut-Out While Driving; Electrical Causes
Engine Cuts Out at Speed: Ignition Power Stage Failure
Poor Power; Poor Engine Response
Intermittent Ignition Shutoff: FI Relay or Ignition Switch
Unexplained Driveability Problems with ECU Error Codes; Oxidized Connectors
Unexplained Driveability Problems: Rotten Battery Cables
Unexplained Driveability Problems: Bad Voltage Regulator
Car Runs but Won't Re-Start; Bad RPM Sensor
Car Stalls When Brakes Applied: Vacuum Leak or FI Relay
Car Stalls at RPM: FI Relay or Hall Sensor
Rich-Running Problems:
Rich Running Problems: General Diagnostic Notes
Car Stalls; Bad FPR Likely Cause
Car Stalls During Turn; Bad Fuel Pre-Pump Likely Cause
Poor Performance; Rich Mixture Smell: Diagnostics; Faulty FPR
Poor Perfomance, Bad Acceleration: Faulty FPR
Engine Hesitation: Bad FPR
Fuel in Oil: Faulty FPR or Injector
Other Running Problems:
Car Stalls Repeatedly on Startup: Fuel Pump Check Valve
Car Stalls, Lights Die: Electrical Ground Fault
Car Over-Revs RPMs While Under Acceleration
LH-2 Cold Idle Problems -Bad ECT or O2 Sensor and Wiring Harness Notes
Car Won't Start: Neutral A/T Safety Switch at Fault
Car Won't Start; Plugged Catalytic Converter
Turbo-Specific Symptoms:
Turbo has Poor Acceleration; Diagnostics
Turbo Suffers Severe Misfire: Leaking Intake System
Engine Cuts Out; Rich Running: Turbo Electrical Harness Degradation
760T Misfires; FI Resistor Pack Defective
Hot Start Problems: Faulty Hall Sensor
Hot Start Problem: Power Stage Overheats
Diesel Engine Symptoms (see Diesel section)
960/90-Specific Symptoms (see 960 section):
960 No-Start: Sticking Valves
960 Stalls: Wiring Harness
960 Sudden Idle Surge: ECT Sensor Failure
[Editor: 960/90 series cars suffer from numerous wiring and electrical troubles, all explained in the 960 section.]
Emission Control Problems (High HC, CO, NOx):
Emission Control Problems: High HC, CO or NOx
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Abbreviations:
AMM Air Mass Meter
ECT Engine Coolant Temperature sensor
ECU Engine Control Unit computer (either fuel injection or ignition)
FI Fuel Injection
FPR Fuel Pressure Regulator
IAC Idle Air Control solenoid valve
TB Throttle Body
TPS Throttle Position Sensor
VSS Vehicle Speed Sensor
Idle Problems:
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Poor Performance, Idle Surge and Hunt: Dirty Throttle Body. Low or hunting idle, frequent stalling.
[Diagnoses:] Please try cleaning your throttle body (TB), it can make a world of difference and save you tons of money. If your B230FT throws oil around like mine, the throttle body can easily get crudded up and cause problems exactly as you described. I thought I had a clogged cat, a clogged intercooler, bad O2 sensor, bad AMM. All these were fine, just a dirty throttle body caused the problem.
[Notes and Tips: illustration copyright RPR, used by permission]
Buy a new throttle body gasket. Disconnect the wiring harness from the throttle switch by compressing the wire bail on the connector body, then pulling the connector straight away. Disconnect the vacuum lines. Disconnect the throttle actuator rod by using a small flat-bladed screwdriver to gently pry away the little locking tab on the end of the lower ball-and-socket. Use a flashlight to see it better. (The plastic ends which have the socket & ball attachment on the link rod can break when they are removed from an old or very cold engine, so be very gentle and don't work on a frigid piece of cold plastic. Get replacements from the dealer. One is a right-hand thread, the other left-hand.)
Unscrew the three nuts holding the TB on to the intake manifold. You may need a magnet here if you drop one. Remove the throttle body from the intake manifold. The gasket on my car lifted right off with no fuss, but if you have to scrape be sure to use a plastic or wood scraper so as not to damage the aluminum facing. You can reuse the gasket if it is in good shape.
Clean the entire throat and the throttle plate paying particular attention to the edges and pivot points to make sure it can close completely. Use an old tooth brush and spray fuel injection (not carburetor) cleaner. Remove the base idle black adjusting knob if so equipped and blow out that passageway and blow out another bypassing passageway that you will see in the throat. Clean out the vacuum fittings at the top. Avoid getting cleaner in the black throttle switch. If you don't have an air compressor to blow out the passages, use the spray tube on the FI cleaner can for that. Of course you will want to clean the outside of the throttle body so it will look nice. Assemble in reverse of disassembly. The holding nuts go on tight enough to prevent air leaks at the gasket, but don't overdo the torque in the aluminum manifold. I like to lube the ball-and-socket ends to free them up next time I clean the TB.
[from a Jag owner] The engine breather is plumbed in upstream of the butterfly. The fumes from the breather are carrying oil and combustion vapors. When this stuff attempts to past the butterfly in the mostly closed state, the pressure (and hence temperature) drop causes the fumes to condense out of the air stream... sticking to the walls of the throttle housing right around the butterfly... a petroleum snow storm. As an aside, this buildup can cause really weird problems on cars with automatic IACs (idle air control: idle speed control). The gunk will restrict the air flow through the butterfly, forcing the IAC to open farther to maintain a proper idle speed. On some cars, you end up with the IAC operating well outside it's designed range... resulting in a major ring/hunt. Killer surging. Oh, and since the butterfly is plugged, all of the air, and breather fumes, pass through the IAC. The snowstorm happens in the IAC, ruining it. Do NOT adjust the throttle stop! Clean the gunk out every 15K or less on cars such as Volvo.
Note on Throttle Body and TPS Adjustments. For more information on adjusting idle speed on 1989+ LH2.4 cars, see Throttle Body and Throttle Position Switch Adjustment. This expands on the notes below and presents the official procedure for adjustments.
[More on Routine TB Cleaning, 92 940:] Try cleaning the throttle body with fuel injection cleaner in a pressurized can. You need to unclip the throttle linkage from the TB (see tips above regarding not breaking the clips), unclip the idle/full throttle switch plug, disconnect the two vacuum lines and the 3 in rubber hose, unscrew the three nuts holding the TB on. Run carb cleaner through there, clean all varnish off. Use a toothbrush if needed. Don't spray the cleaner on the TPS. There are tiny inside vacuum holes that lead to the vacuum tubes that may be completely plugged. Check the gasket (it will probably be useable once or twice more) or replace it, and put everything back together. This off idle bog happens on my 760T every 5-6K miles when the TB gets crudded up.
One of the threads recommended removing the idle switch assembly when cleaning the throttle body. DO NOT DO THIS unless you want to mess up the setting and have to readjust it!! I've cleaned several throttle bodies on LH-Jetronic FI systems dozens of times and have never had to remove the idle switch or had problems with it. Just don't soak it in carb cleaner.
But if you can't help yourself -- take a small screwdriver or other object that will make a fine scratch and scribe a line across the edge of the throttle sensor switch's flange and it's mounting bracket, right where the Allen screws hold it tight. Doing so will get you in the ballpark when it's time for reassembly. After re-assembly, be sure to check for the "click" when the throttle butterfly comes off its stop, and adjust as necessary.
[Tips on aligning the TPS on re-installation:] Check the idle switch on the TB before you do anything...you should hear a distinct click RIGHT as the throttle is opened signaling the switch is telling the ECU the engine wants off idle NOW. If this switch is even an RCH slow, so will your off idle response. See the section Throttle Body and Throttle Position Switch Adjustment for more information.
[Tips on reassembly of TB shaft spring:] I carefully took the spring off the side of the throttle body, noticing that it was under tension... one full turn, but alas... I forgot to note if it was under tension one full turn CLOCKWISE or COUNTER CLOCKWISE. [Response:] The throttle body spring, attached to the throttle body lug that goes into the throttle body and points out from the throttle body to the radiator goes CLOCKWISE! The spring has a little bent-out stop that catches under the idle adjustment screw. You put the spring on so that catches... twist the dang thing one turn clockwise, put your nut on, attach the throttle control rod and it's done.
[More on TB and TPS Adjustments from Gregg Stade] The mechanical stop is a setscrew on the forward side of the TB aimed up. It has a nut (8 mm, I think) on the underside. It's right near the big coil spring that turns the throttle to idle. When you turn the throttle and allow it to return to idle position, you can see a small arm bear against this setscrew.
The throttle switch is on the backside of the TB, opposite the setscrew, and is locked by two small screws. It has an electrical cable plugged into it.
With the TB off the car, I first loosened the switch so it didn't inadvertently act as a stop (very bad for the switch!). I backed the setscrew out until the throttle butterfly plate was completely, jammed shut. Then I turned the setscrew in until it just touched the arm, and another 1/4 turn. This takes the mechanical force off the butterfly, so when the throttle slams shut, it doesn't wear the butterfly or damage the switch. Don't forget to tighten the locknut, and then recheck the adjustment -- tightening the locknut can change the screw position slightly.
Then, with the throttle at idle position (the spring forces it there), you carefully turn the switch until it goes "click". Tighten the two screws. Be sure, as you rotate the throttle (TB still in your hands) you can clearly hear the switch "click" and that it does it while the arm is maybe 0.030" off the setscrew.
[Adjustment of Pre-89 TB, TPS and Base Idle:] The p/n's for the gaskets you will need are 1271488 and 463766. There is an o-ring on the black knob (pre-'89 only) that you will have to remove to thoroughly clean the housing p/n 947114. Do not remove the throttle cable, but with a small screwdriver unclip the small plastic linkage lock from the throttle body and swing it up , then disconnect the throttle switch . After the housing has been cleaned the throttle stop is adjusted. Loosen the 8mm lock nut and back out the screw, turn the screw back in just till it contacts the lever. Rotate the screw another 90 degrees and lock it down. Install the throttle switch and rotate it till it clicks with the throttle plate closed. Lock it down, the switch should make a click as soon as the throttle plate is moved . Test it several times in your hand at varying opening speeds make any fine adjustments now. BTW don't loose the o-ring on the switch if you remove it; it is not available as a spare part. With the housing back on the car, adjust the linkage rod so that the throttle plate doesn't move when it is hooked back up. After everything is hooked back up there are two more things to do. First, adjust the cable with the threaded piece at the throttle bobbin. You just want a little slack. Second, base idle has to be reset. (Pre-1989 only:) For this, you will need a tach/dwell meter. You need to read engine rpm. Warm the engine to operating temp. Here s the tricky part. There is a blue connector behind the battery with nothing plugged into it . There should be a blue/white wire in the connector. Ground this wire it shuts off the idle speed motor so that base idle can be adjusted with the black knob on the throttle housing. Base idle for this car should be 700 rpm. When the ground lead is disconnected the idle should go up to 750rpm's +/- 20 rpm's.
[More on Setting Base Idle Rate:] Just adjusting the base idle by the set screw is not a good idea. First, you must check to make sure the throttle housing is clean from oil deposits, as above. Upon re-assembly, the base idle set screw must be backed off, then turned in till it just touches the housing. You want to turn the screw 1/2 turn then lock it down with the 8mm nut. Remount the throttle position switch and rotate it just so it clicks then lock it down. In 1989, Volvo did away with the black idle speed screw, everything is controlled by the fuel ECM .If the throttle plate doesn't return completely and energize the TP switch, the fuel ECM doesn't know the throttle has returned to idle.
Note on Use of Solvent Cleaners. [Larry Carley, Brake and Front End Magazine, Dec 02] Using conventional aerosol carburetor cleaning solvents on fuel injection throttle plates, for example, can be an extremely expensive mistake. Although strong solvents instantly dissolve gum, varnish and carbon from throttle plates and bores, they also dissolve throttle shaft seals, throttle position sensors or (when applicable) the Teflon from the air inlet horn! Nevertheless, specially formulated throttle body solvents do as good of a job without causing potential driveability complaints. Most are also good for cleaning delicate import carburetors for the same reason. Unlike "killer" carb cleaners, throttle body solvents don’t cause comebacks by eating away at delicate switches, potentiometers and neoprene diaphragms found on import carburetors. Most throttle-body aerosols also spray in the inverted position for cleaning hard-to-reach components.
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Poor Idle; TB Cleaned; Now Idle is Too High. [Query:] Well my problem is certainly gone. It now idles at 1600 rpm, but that's a steady 1600. Did I do something wrong, or was the crud in the throttle body masking another problem? The barrel of the actuator rod is threaded on both ends, did I loosen an end accidentally? Should I take it back off and remove the spring assembly from the side of the body? Since mine had a very short assembly on the side, is that the idle adjuster? How is it adjusted? Thanks for any help anyone can provide. [Response: Evan] Nope, the crud WAS the problem. Crud makes the car idle lousy and slow. Lazy mechanics simply dial up the idle to mask the problem, rather than fixing it. You just need to dial the idle back to spec. On the end of the butterfly shaft, the end where the spring is, there's a stamped metal plate. It has a 'leg' bent down that rests against the idle stop screw. The screw is held in place with a lock nut. loosen the nut and adjust the screw. [See Throttle Body and Throttle Position Switch Adjustment for more detail on 89+ cars and Adjustment of Pre-89 TB, TPS and Base Idle: for pre-89] Be careful, the screw head has a tendency to strip out. In retrospect, you should have taken a minute to make sure the screw was free while the TB was on the bench.
Another thought: Before you do any of the above, make sure that the 'leg' on the stamped metal plate actually touches the stop screw at idle. Some REALLY lazy mechanics just adjust the throttle cable length at the big obvious pulley, rather than adjust the stop screw
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Poor idle, Smoke, Oil Leaks: Clogged Flame Trap [Symptoms:] Smoke out the tailpipe, gradual oil loss, fouled plugs, valve cover gasket or main oil seal leakage. [Tip: Bob Savasta, Motor Magazine, Jul y 2001] These are classic symptoms of a bad PCV or flame trap system, which is clogged with sludge or carbon.
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Fuel Intake Carbon Removal.
Problems With Valve and Injector Deposits. [Motor Magazine, Dec 2002] As a vehicle approaches higher mileage, you can generally expect intake valve deposits (IVDs) and injector deposits. Their onset can vary widely, depending on driving conditions. Engine operating temperature, intake manifold gas speed (rpm) and hot soak cycles are some of the critical operating parameters affecting these deposits. To lubricate an intake valve, tiny amounts of oil have to run down the valve stem. Over time, this oil is deposited and heated on the intake side of the valve, forming a carbon cone. This has multiple effects on the intake event. The carbon changes the aerodynamics of the intake event - causing higher gas speed and a change in the direction of intake and swirl - which affects the combustion process. The IVDs also act like a sponge, creating a delay in fuel control. This delay not only creates a temporary enleanment on acceleration but also causes a temporary enrichment on deceleration. When the throttle is closed, the intake manifold vacuum goes high, pulling the fuel out of the carbon sponge. This affects fuel control. When the engine is shut off, a small amount of liquid fuel is left on the tips of the injectors; this fuel evaporates and leaves behind solids that were originally dissolved in the fuel). Eventually, these deposits cause an injector to act like a squirt gun rather than an atomizer. Aggressive drivers and drivers with long highway drive cycles may not have deposit issues until very high mileages. Stop & go drivers, especially delivery drivers with many hot-soak cycles, are more likely to experience deposit problems sooner.
See the FAQ Section on Fuels and Lubricants for more information.
Carbon Removal in Injectors, Intake Manifold, Valves and Cylinders.
Gasoline Additives. BG44K is the heavy duty stuff - and recommended in Volvo and BMW TSB for removing carbon deposits, particularly from intake valves and fuel injectors. Use no more often than 2/yr, and only 1/yr if your system is in reasonable condition. Pour the can in the gas tank only with the tank full. Use it when you will be able to drive out a tank of gas in a day or two. Plan on changing the oil and filter soon after use as it can contaminate the oil with unwanted chemicals. Distributor at website: http://www.bgprod.com . Other effective products include Chevron's Techron, STP's Complete gas treatment, and GM "Top Engine Cleaner". Using these cleaners in conjunction with an "Italian Tuneup" (driving at high rpms while the engine is fully warmed up) is frequently very effective. [Caution from Zippy] Volvo specifically recommends AGAINST using any fuel or oil additives. I know they used to suggest it was okay, but then decided that catalytic converter damage is done when additives are used. Since about 1993 gasoline improvements have made additives unnecessary.
Cleaning Machines. Snap-On decoking machine (reported very effective by Robert Price) It does clean injectors but it removes carbon better! Also, try Motorvac (a variation on the Sun machine.) Other techniques include walnut shell blasting/flushing (many sources of good success) in a shop with the equipment, most often a BMW specialist.
Injector Cleaning. See the FAQ section in Engine: Fuel Injection for tips on injector cleaning.
Combustion Chamber Deposit Removal. See the FAQ section in Engine: Mechanical for a water-based technique that works, although using it with turbos may be a bad idea.
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Engine Dies After Starting, Won't Idle; Needs Intake Cleaning. My '85 with 230F had a similar problem. It would die after starting and put into gear when cold and Idle was not stable. Here's what I did to fix it:
Replaced all vacuum hoses and checked for vacuum leaks.
Removed and cleaned air control valve.
Removed and cleaned throttle body in fuel carb cleaner, replaced all gaskets.
At this point it was running better but not perfect.
Adjusted throttle body linkage and throttle position sensor per the book. It has to be done in sequence.
Ran a can of BG44K through the tank to clean up intake valve and fuel system deposits.
Car now runs very strong.
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Poor Idle: Injectors Need Cleaning. See Injector Cleaning for more information on how to solve chronic idle problems due to dirty injectors.
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Poor Cold Idle: B230F/T ECU E-Prom Needs Update. [Query] My wife's 95 945T (90k miles) starts fine on a cold (below 40F) start, but idles like crap for 20 to 30 seconds. If I hold my foot on the gas and keep it at 1500 rpm for 8 to 10 seconds, its fine. Car idles nicely when warm, and runs like a dream. When I pull the plugs, they look great. I've replaced ECT and other parts and cleaned the TB. [Response: Abe Crombie] Go to a dealer and have them look at Volvo Service Bulletin 28-102 "modified e-prom for cold start with low rvp fuel". This says the symptoms are: car starts and then immediately dies and requires re-start. Runs rough for the first 45 seconds and may hesitate on acceleration. Recent EPA regulations have necessitated changes in the formulations of gasolines (i.e. "oxygenated fuels"). The result of these reformulations has been a decrease in the relative vapor pressures (volatilities) of these fuels, which seems to be particularly problematic for cold starts/idling. The updated eprom chip to be installed in the ECU is the fix to make it have correct fuel mixture computations for cold start. You must have the number from your ECU in order to cross-reference the correct eprom update kit P/N. The change procedure described in 28-102 requires careful attention to static discharge.
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Idle Speed Control Problems.
High or Unstable Idle. [Symptom] My 945T (94 - 99k) has been having high/low idle problems - it wanted to idle around 400 or 1500+ - there was no middle ground. [Solution] Replace the throttle position switch, which detects idle when the switch is closed and, if faulty, will cause idle problems.
Idle Speed Control on Late 7xx/9xx. In Volvo 700/900 cars with LH2.4 fuel injection, the idle speed is controlled by a bypass system. When your foot is off the gas, the throttle plate is fully closed and a separate idle air control valve admits the required amount of air to get the engine to idle at 750 rpm. This separate valve is controlled by the computer. No adjustments are possible.
Start or Stall Problems:
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No Start; Frequent Stall or Hesitation: Basic Diagnostics. [Query:] I have an 88 740 non turbo 150k miles. Intermittently the engine will stall typically at lower speeds or idle. It will not restart unless I turn off the ignition and back on again as if this resets something (the computer?). Also there is a stumble or miss when starting out from a stop. This is fairly consistent. Another symptom is that intermittently at cruising speed of say 60mph the engine appears to cut out for only a half second, this will continue several times a minute until I shut off the engine and restart. Plugs and wires good, throttle body clean, fuel pressure OK, O2 sensor OK, have checked all connectors that are easy to get at. It appears that the computer sometimes gets out of whack for some reason and wants to be reset. Any suggestions?
Basic Diagnostic and Preventive Maintenance Checklist [from Paul Grimshaw/David Hunter]
You've either got a fuel or spark problem. Here is a basic diagnostic checklist:
Watch the tach carefully when a stall occurs. If it drops to 0 even before the engine winds down then that would indicate loss of ignition pulses to the coil negative terminal. Primary suspects would be the power stage or the crank position sensor. If tach tracks the engine speed as it winds down then that would indicate a fuel injection problem. Suspect radio supression relay or loss of fuel pressure due to relay or pump.
Confirm condition of distributor cap, rotor, spark plug wires and spark plugs. If *all* of these have not been replaced in the past two years with OEM or better (ie. higher quality ~ more expensive), do so now. (Yeah, I know that you have not yet determined that the problem is spark related, but there's no sense troubleshooting a problem unless the basic bits of maintenance are completed and certified correct).
Remove each spark plug, ground the threaded base against the engine block and, with the spark plug wire connected to *only that plug*, have a friend crank the engine. You should see a spark. If not, there is a problem with spark delivery. Repeat with each plug/wire. Note: In most cases, its not the spark but the fuel. That said, any failure to complete basic maintenance on your engine will only lead to a poor running engine and multiple, intermittent faults.
If your have not replaced the fuel filter in the past 3 years, do so now. The fuel filter/fuel pump is located under the passenger footwell (driver's side). Replacing the filter is not a particularly difficult job for the experienced shade tree mechanic with a complete set of hand tools. If you're unsure of your experience level or tool crib, have the job done professionally. Ensure that the sub-assembly is completely cleaned and dried before disassembly as FI systems do not react well to ingested dirt. It will require Volvo PN 1389562-8. While you're replacing filters, don't forget the air filter -- you engine will always run better with a new one of these! Again, a bit of basic maintenance that should never be skipped.
If you lack a fuel pressure gauge capable of reading fuel pressure to at least 400 kpa and lacking the proper fittings, true troubleshooting will be difficult. Your car's LH system is supposed to operate at a constant 300 kpa.
Lacking the proper diagnostic equipment, your only solution will be to replace each component until the problem is solved. I won't list all of the possible problem components as most situations are traced back to either the main fuel pump or the pressure regulator. Use a long piece of hose to listen for the main fuel pump as the car is being cranked. If you cannot hear the fuel pump turn, check the voltage using a VOM.
If all is well, skip to the fuel pressure regulator. Replace the unit with Volvo PN 1389564-4, but may also be replaced by Bendix PN 4088942-0001.
If the car now runs, but frequently requires long periods of cranking to start, then suspect the check valve in the fuel pump. The check valve is a threaded in-line valve that maintains line pressure between 200-300 kpa after the engine is shut off.
If the car still does not start, check the fuel pump relay. If in doubt, replace it with Volvo PN 3523608-3.
If the car will not re-start while warm, check the radio suppression relay and the rpm sensor (LH2.4) or Hall sensor (LH 2.2).
If the car stalls while hot, check the ignition power stage amplifier which is cooled through body contact.
Regina-Equipped Cars: Check as well the coil pack and MAP sensor.
Conclusion. The beauty in the approach listed is that you first complete the basic maintenance required; car's just won't run well without regular maintenance! Second, you're using a rudimentary tool (the hose) to check for fuel pump operation. That's important since the fuel pump is a very expensive piece of gear that you would not really wish to replace unless it is dead. Third, there's some merit in repair by replacement, especially if you lack the proper fuel system diagnostic equipment. The pressure regulator is about $40 buck and, with age, will eventually die anyway. So replacing it just saves you being stranded at some point in time. Finally, the pump relay is the next most likely culprit. [Editor's Note: See the notes below about rpm or Hall sensor and radio suppression relays; these can also be frequent culprits.]
Hope this helps. Remember the merits of maintenance before trying to solve any recurring problem.
Basic Ignition and Fuel Injection Component Diagnostics. My '87 740 GLE routinely dies. My mechanic tells me there is no injector pulse with the hall effects switch or the fuel injection control unit being the most likely causes. Is there any way to test these components?
[Tips from Bob Dietz] When the car dies run a test light from the negative side of the coil to ground. If the light flashes brightly when you bump the starter then all the ignition components are ok, and the fuel pump should run for a few seconds. If the light barely flashes and the fuel pump doesn't run, then suspect the ignition amplifier (between the air filter housing and the inner fender wall.) If the light flashes and the fuel pump doesn't run, suspect the fuel injection relay (the white relay behind the ashtray--remove the lighter, lighter cover plate, two screws and the ashtray to access). Pull the cover off and reinstall, turn the key to run position and operate the contacts by finger. If the fuel pump runs then the relay is suspect--resolder or replace--your choice. If by turning the key to start and holding the fuel pump point set closed the car runs, release finger pressure on the fuel pump contacts. If the contacts stay closed for a few seconds after you release the contacts then the relay is bad and the fuel injection control unit is ok. If the motor shuts off as soon as the fuel runs out after you take finger pressure off the relay contacts then replace the relay and the fuel control unit--the protection diode on the relay has failed and wounded the computer.
Other Component Tips:
[Tips: Mark Klein] Sounds like you've been fairly thorough already. There is a radio noise suppression relay on the coolant reservoir which can go bad and cause a variety of similar symptoms including not running at all. Be sure the fuel pump relay is in good shape. It is the white one in the 2nd row back on the far left. Check the date code printed on the side. If it is the original, it wouldn't hurt to replace it anyway. The Hall sensor sender wiring (pre-89 cars) coming out of the bottom of the distributor can short out against the distributor housing if the plastic connector breaks. This is quite common but I doubt if this is giving your symptoms. The rpm sensor on later LH 2.4 cars can also fail. The FI control unit itself can go bad. One of the more common circuits which fails is the one that grounds the fuel pump relay and, in turn, turns the fuel pump on.
I doubt if an air mass meter would give the symptoms you're getting but you might try removing and reconnecting the electrical connector a few times.
Wiring Shorts. [Tip from Chris L] Stalling combined with fuse 11 failures (fuse 11 supplies the fuel pump and the oxygen sensor, at least in Regina cars) can result from wiring shorts at the fuel sender unit at the tank or in the oxygen sensor heater wiring near the exhaust, which can fray and short against the pipes, causing the fuse to blow.
Carburetted Engines. See the note regarding relays below. Don't immediately conclude you need a rebuilt carburetor.
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No or Slow Hot Start: Problem Diagnosis and Repair. See the attached file for a quick-reference guide to no- or slow-hot-start problems and diagnoses.
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Intermittent No Start or No Warm Restart: Radio Suppression, FI Relay, RPM Sensor. [Query:] Sometimes the ’88 749GL just won't start. It seems like it's not getting gas when this happens, but after sitting for awhile (a few hours, overnight, or occasionally just a few minutes) it starts right up like nothing is wrong [Editor:] If your car fails to start until after it has cooled down, the three items to check are the rpm sensor, radio suppression relay and fuel injection relay solder joints. [Response 1:] Try the fuel injection relay. Find the relay in your center console relay bank and tap it to see if this restores fuel flow (starting immediately). [Response 2:] I have a 90 740gl that had the same problem. When you're cranking the engine and it won't start, is the tachometer needle moving a little? If not, as mine didn't, I believe you want to check into the RPM sensor. Check the RPM sensor located on the back of your engine, connected to the bell housing. The wire runs up the back of the engine compartment towards the drivers side. Look for the part number on the wire and check if the part number ends with 399. This rpm sensor has a heat related problem: common for it to cause a no- start but able to start a little while later. Since I replaced mine for about 30$ I haven’t had the problem. [Editor: post-88 cars have this sensor; pre-88 cars have a Hall sensor inside the distributor.]
Tach Needle Movement. [Chris Herbst] In all of the Bosch systems, the tach jumps when you crank the car. In the Regina systems the tach does not usually move until the car is running. I have noticed this in all the Rex ignition ('Regina') cars. Unless the car is running, the tach is normally lifeless.
If you Have a Regina System: [Chris Herbst] If you have problems with a Regina system that has an intermittent no-start:
Crank sensor
Interference relay
Fuel pump relay
Coil pack (THIS IS A BIG ONE)
MAP sensor. Not very expensive.
Far Less Frequent But Still a Related Symptom: Ignition Amplifier. If the car will start and then die, or refuse to start again until it's cooled off, or just not start period. or just randomly die or misfire under load, then suspect a failing ignition amplifier. This is located on the driver's side fender (wing) behind the headlight.
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Intermittent No Start: Fuse Contact Failure. [Tip from Roman Shestakov] I had a situation when my 1990 740 GLE just would not start. Engine turns, lights come on the dash, but does not start at all. No pre-charge noise from the fuel pump could be heard before turning the engine. After pulling out the relay tray to inspect the fuel injection relay, I found instead that fuse #1 that supplies power to ECU and fuel pump was making bad contact with connector in fuse box. Plastic around that fuse was melted and looked brown. You immediately could tell that there was an excessive heat around that fuse. Repairing it was easy. After pulling the fuse/relay assembly box out of console, remove all fuses. Take a flat screw driver and pop the fuse box upper cover out by prying on its sides (there are already slots available for that kind of tool), exposing fuse contacts. Examine the fuse contacts. Mine were all oxidized and looked very brown (heat caused copper to oxidize and made contact surface even less conductive over time) causing current to heat up the contacts. Take a small piece of sand paper (spread contacts apart with screw driver if necessary) and clean contacts inside surface from deposits until it turns copper-red like other contacts next to it. In my case, I had to scrape them with a knife as well. Then straighten contacts carefully so that they are parallel to each other and "lean" against each other as tight as possible, similar to undamaged fuses. Your fuel injection fuse is rated at 25A and must go in tight, or you will be facing the same problem again. Then pop the top cover back on and reinstall all fuses. Re-install everything back into console except the fuse cover box. Test drive the car for 5-10 minutes, and while you are driving, put a finger on fuse #1 and the plastic upper plate around it. It must be cool to touch.
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Intermittent No Start: Washer Fluid Line Leaking Onto Distributor. [Tip] My 940 suffered from intermittent no starts until I discovered that the windshield washer fluid anti-check valve on the firewall was leaking and squirting water onto the distributor cap. A new valve, cap and rotor solved the problem.
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Intermittent No Start: Battery Ground Connector Failure.[Query] My 1988 740 GLE has been having an intermittent no start problem; all other causes have been ruled out. [Tip:Dan] I would follow the battery ground cable to the block , it is just in front of and just below the oil filter. Pull on the cable hard while wiggling it. I had the same symptoms as you have and in my case that was the problem. When I just touched my cable at the block, where it went into the connector it came right off in my hand. I bought a new one of the correct length and re-routed it, instead of running back through the frame, where by the way, the plastic insulation was worn completely off to bear wire. That is what caused my start sometimes and sometimes not. [Editor] Check your engine ground straps for oxidation and corrosion.
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No Start; Tear in Air Duct Intake Hose. [Query: David Smith, courtesy UK Volvo Club] For the last six months it has been getting harder to start. Up to now there has been no problem - has 170,000 miles. Fuses are OK and I replaced the distributor cap, rotor, installed a new wire set and replaced the spark plugs. I also noticed that one of the wires leading to the coil was also in very bad shape at the coil end. I snipped off some of the wire and replaced the female connector. I’ve been to two dealers who put it on the computer ‘scope’ - no problem shows up. One dealer cleaned the throttle body (dirty) and the other installed a new crank case sensor. A third dealer said it may be a poor ground (all seem OK) or a computer module. I said that nothing showed up on the computer analysis at two different dealers - and he said that it probably wasn’t the module in that case. Very recently it just wouldn’t start. It turned over OK and I unsuccessfully tried to jump start it from two different vehicles, a light truck and a V8 Chevy (using a good jumper set). There was spark from the plugs when turning over. We also sprayed di-ethyl ether in to the engine via the fuel injection system and engine fired OK when turned over. Tried again - turning over OK - but not starting. However, just three hours later it started up with no problem on its own and has run OK for 3 days. From what I can gather I suspect that it may be an ECU problem - but nothing has shown up on the computer scope at two dealers. [Later reply from David:] A local mechanic found a small tear in the large diameter air hose (has the bellows) that runs from the air mass sensor (and air filter end) up to the throttle body. He did a quick repair using a sealant. Since then everything has been fine - no more starting problems. It's very easy to inspect this air hose - just undo the clamps at either end - make sure they are tight when you put the hose back on! I spoke to another Volvo dealer recently - regarded as the best in Toronto - and they said that this air hose vibrates - hence the need for the bellows section. In addition the material used to make the hose does start to perish over time and this may lead to some brittleness and tears appearing. When that happens - it can lead to all sorts of problems they claimed. The replacement hose costs just $50 Canadian.
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Frequent Stall or Hesitation: Carburetted Engines. [Tip from James] My 1986 740 with B230K (carburetted) suffered from a constant stalling problem, needed to be revved all the time. Following the dealer's advice, I installed a rebuilt carburettor which did not solve the problem. I found that a relay had burnt out that controls the idle solenoid/cut off valve/intank pump/ IAC. The relay is green and about 2 inches long by about 1 inch deep and one could quite clearly see the burnt-out solder joints when it was opened. I fitted a new one for £32.00 including the diagnosis and this solved the problem.
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No Start, Poor Fuel Economy: Timing Problems [Tip from Tom Francis] Poor fuel economy and then a perplexing no start situation was the result of a broken indexing pin (roll pin) in the end of the cam shaft used to keep the cam pulley and the cam shaft in alignment. The broken pin allowed the cam to rotate out of alignment 30-40 deg until the no start condition. Remains of the hardened steel pin in the cam can be drilled out using solid carbide drills bits in successively larger sizes, but not large enough to ream out the hole. High speed steel or carbide tipped drill bits may break off in the hole. The roll pin is most likely a standard M5-80mm size (5mm dia hole, 80mm long), available from a dealer for $0.90 or well supplied hardware store. [Editor] This applies as well to the crank timing gear, which has a similar indexing pin, and is a very good argument for using the correct torque procedures when reinstalling the cam or crank bolts.
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Stalls in Heavy Rain: Water Leak in Hood. [Tip] I finally figured out my stalling problems after a heavy downpour (ie, Tropical Storm GASTON and FRANCES) My 940 once again stalled on me about 5 miles away from my house... This is the second time in a row and it was after a heavy downpour, with water leaking onto the distributor cap. After examining the hood weatherstripping, I found that the water was pouring down through the windshield washer nozzle hole in the hood. Sealing this with silicone caulk solved the problem.
Mixture, Misfire or Idle Control Problems
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Runs Rich; Black Smoke; Poor Acceleration: ECT, TPS, FI. [Query:] I have a 1985 740t with 244,000 miles and a m47 manual transmission. It has the 230ft engine that is all original including the non-liquid turbo without an overhaul. The car runs rough throughout the rpm range and put out black smoke while doing so. Lots of black smoke. Other times (less and less) it runs like a top, no problem. I replaced the fuel pressure regulator but it did not help. I am getting about 43psi at idle. When it is running in the bad mode the fuel pressure is still 43psi. When I drive the car I have to accelerate either very easy or in wide open throttle to get the car to go. It is at its worst just as boost comes on. Any Ideas? [Response 1:] Here's one idea, but it really applies to the non-turbo engine -- so I could be a million miles off base on yours....... The fuel mixture is influenced by the block temperature sensor (Engine Coolant Temperature ECT see Diagnosing ECT Failures ). A cold engine requires more fuel, and a warm engine needs less fuel. A cold sensor is a high electrical resistance. An intermittent open condition of the sensor, the connections, or the wiring harness will "trick" the FI ecu into thinking it's about -60 degrees. It will pump in tons of fuel. On many of the engines -- and again, I'm not positive about yours -- there are two sensors. The sensor for the dash gauge is in the head, about under the intake runner for cylinder #2. The sensor for the FI system is in the head, about under the intake runner for cylinder #3. Tough to get to.
I helped fix a situation (on a '90 740, non-turbo, Rex-Regina system -- yours is Bosch) where the connector had pushed out of the plastic housing but made intermittent contact with the spade connector in the sensor. Some days, it ran great. Other days it flooded so bad it wouldn't always start. Fixing that stupid problem made a world of difference!
[Response 2:] Also..... be sure the throttle switch (Throttle Position Sensor TPS) is working and adjusted, and the AMM is operational.
[Response 3:] Very similar situation in my '86 745T drove me nearly crazy for about 2 months. It was a leaking fuel injector
Symptoms of ECT Failure:
[Tips from Isaac Babcock, who disconnected his ECT to find out]
Difficult cold starting. Approximate crank time 4-5 seconds.
Extremely difficult hot starting. Cranking 20 seconds may or may not yield a running vehicle.
Once started, car idles like absolute crap for 5 minutes while the engine burns out all the excess fuel that the computer is blindly dumping in. May die repeatedly during this time. Small amount of black smoke flows from tailpipe.
During 5 minute crap idle time, car will not tolerate any accelerator input. Depressing accelerator kills the car immediately.
After the 5 minute extreme fuel enrichment exercise, the car lets out its last puffs of black smoke and you can drive off.
Idle once engine has 'stabilized' is a fairly steady extremely high idle. It will be quite noticeably higher than normal (over 2,000 revs). I thought my computer had fried the IAC motor circuit with it stuck full open. Turning the idle bypass screw all the way closed can only bring the idle down to 1250rpm.
Smell of unburned fuel floats around car at all times. Gas mileage is atrocious under all conditions. I achieved 16-17mpg on my last tank.
Power is fairly crappy, though not much worse than usual.
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760T Floods and Stalls: ECT?. [Query:] I have a 1986 volvo 760 turbo with 207,000 miles on it. I recently purchased and at the time it was running on three cylinders and had sat for about six months. I replaced the flux amplifier and it ran on all cylinders. The man who sold it to me also told me that he had an intermittent problem... It would stall out occasionally. He was true to his word...If it is cold (running about 15 min. ) and you give it too much gas it starts to flood out. If you floor it while it is flooding out it starts to catch on the other cylinders and eventually will go. If you stop the car while it is flooding out it will either stall or run on 1 or 2 cylinders. One time I disconnected the map sensor while it was flooding out and it started to idle normally. While driving behind the Volvo it spits black smoke when it is flooding and sometimes even when it isn't acting up a little bit of black smoke will come out of the exhaust. The problem clears up if you drive about 30 miles on the highway at constant speed. After that you can stop it idles pretty good.... misfires a tiny bit.... and you can take off like a bat out of hell...also about a week ago I tried to start the car and it would only run on 1 cylinder, then not at all. I pulled the plugs and they were all fouled I put in new plugs and it fired right up. I tested to make sure every cylinder was firing and they were...is it my computer??
[Response: Don Foster] I'd consider looking at the temperature sensor or connections to it. There are two sensors -- one for the temp gauge, one for the FI ecu. The gauge sensor is a one-wire device, the FI temp sensor is a two-wire device. The FI temp sensor is mounted in the head, under the intake manifold, approximately under runner #3. It's not impossible to get to -- just almost. (The gauge sensor is under runner #2 -- ignore it.)
The sensor is an NTC thermistor -- that's "negative temperature coefficient", or as the temperature drops, the resistance rises. If the sensor fails or if you have a bad, broken, or corroded connection at the sensor (or anywhere in the harness going to it) the FI ecu measures high or infinite resistance. The ecu thinks it's about -100 degrees, and sends tons more fuel to the engine. See Symptoms. And if it's an intermittent problem, your engine can be running fine and then go into gas overload 5 seconds later. And vice-versa. I helped fix a problem in a '90 non-turbo with terrible intermittent flooding. We found one connector in the sensor plug had "loosened" so when the plug was pushed onto the sensor, the connector got pushed back up the plastic housing and sorta dangled freely -- one second it touched, the next it didn't. It took hours to zero in on this tiny failing. See more at Diagnosing ECT Failures
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Cold Start, Dies; Dirty or Faulty IAC. [Symptoms:] Cold Start: Car starts immediately with no throttle application, idles smoothly for about one second, then hesitates and dies. Ditto for my 1990 245DL. Starts up cold for one second, then dies. Sometimes, all cranking I wish to do will not restart it. If I sit and wait about 5 minutes, it will start and run like a kitten, with no problems. I have replaced all spark plugs, s.p cables, rotor, cap. If it is a computer problem, can I fix it? [Suggestions:] Check the IAC (idle air control- This provides for more air, or faster idle on start up. The fact that it starts readily when cold indicates the cold start injector is working properly. See hints below.
[Symptom:] Poor idle. [Diagnosis:] Clean the dirty Idle Air Control Valve (IAC). I should have remembered. The car did not start at ALL. So, I took out, removed the two hoses and cleaned it by spraying it with engine grease remover. It had a lot of dirt in it. The Idle Air Control Valve is located under the intake manifold; below the second cylinder. It is about 3 inches long and about 1.5 inches in diameter (I do not have one next to me so these dimensions are from my memory.) It has two rubber hoses connected to it through a "T" connection. It also has a snap-on electrical plug. This is most likely your problem. Here is how I clean it:
Remove all hoses and electrical connector, then remove the IAC
Open the rotating valve to expose the innards. Spray some carburettor or fuel injector cleaner into the opening and shake it around. Make sure you plug the other end with your palm to trap the liquid inside the IAC.
Open and close the flapper valve with a small screw driver to loosen any dirt, etc. contained inside. Don't scratch the valve
Turn the IAC upside down to empty out the dirt and fluid.
Repeat step 3 through 5 about 8 times.
Test the IAC on the car without permanently installing it. You might have to repositioned some hosing to accomplish this task.
If you still have problems, then either your IAC is dead and must be replaced or the problem is somewhere else. [Editor's Note: See the IAC rebuilding procedure noted below.] [Ian Giles] By the way, when installing the IAC the arrow points in the direction of airflow through the valve, so it points towards the intake manifold.
Poor/Surging Idle: Idle Speed Control Motor. [Tip from Anonymous Source]
I have a 1987 model 780 with about 115K miles. Just wanted to share my experiences:
About 10% of the time my Idle would start to surge between 200 and 1200 rpm while sitting at a light with the foot on the brake. This up and down action would load up the engine with fuel and it would start emitting black smoke. It seemed to be somewhat related to engine temperature. Occasionally it would get bad enough to kill the engine, but at highway speeds it seemed to run fine. I first looked at the idle speed motor, but it appeared to be functioning properly when the voltage was applied to the terminals per the normal checks. I then performed the disassembly and cleaning of the idle speed motor as described in this web site. Even though the inside of the motor was reasonable clean, I went ahead and polished the commutator. I detected that the bearings that the rotor turns on were a bit gummy so I cleaned it well and lubricated it with a bit of graphite. Ever since this little operation it has been idling like a champ. I suspect that small bits of commutator crud and wear on the brushes may have been creating dead spots and poor response to idle demands form the processor.
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Intermittent Stalling: Faulty IAC or Hall Sensor. [Symptom:] Intermittent stalling/no start condition on an 86 740 (b230F) manual trans: occasionally dying (engine suddenly has absolutely no power, but the dash lights do not come on) while driving on the expressway and around town. After pulling over to the side, the car invariably will restart and seem to run fine. No rough idle or other problems were noted.
[Fixes Attempted:] Several months back (per list advice), I replaced the fuel relay, which up until the last week seems to have cured the problem. Over the last couple of days, the car has started acting up again in the same manner. Now, the car also, when it does restart, sputters and runs extremely poor for awhile, then goes back to normal. Also, in the driveway, I was able to get the car to reliably stall when he put on the brakes. I replaced the idle speed motor, which seems to have affected the brake-induced stalling (plus the car idles much better), but not the intermittent stalling. He also noticed a bare temp-sending wire, which he cleaned and re-taped (but we don't suspect that has to do with this failure.) Per past list advice, I've suggested
examining all vacuum lines
rechecking fuel-pump relay and socket for cold-solder joint/overheating socket
in-tank pump and screen
the power stage connectors for corrosion
radio suppression relay
general condition of wiring harness (the car lives in the very heavily salted road conditions of northern Ohio)
[Diagnostics and Suggested Fixes:] Below you'll find several procedures [Composite from Steve McChesney and others]. Hope they will help.
Fix 1: Clean the Idle Air Control ("IAC") Valve. See above for procedure.
Fix 2: Rebuild Idle Air Control Valve: Save $150 by fixing IAC instead of replacing it. (Note: the IAC on newer LH 2.4 cannot be dissassembled but it can be cleaned.)
Symptoms:
No fast idle at start up.
Grounding CIS (test point) does not have any effect on idle. (grounding the test point should disable air control valve (IAC)
OR: The idle ('87 745ti) shoots up to about 2500 RPM. No amount of cooling off, throttle blipping, or general search for vacuum leaks would bring it down. I checked all the hoses, fuel pressure, mass air sensor, and coolant temp sensor. Everything was fine. And the car ran fine too, just a high idle.
This is a common problem on cars that use this Bosch system, including Volvos and BMWs. It's especially bad on turbo cars, and cars that use crankcase air for idle makeup because of the oil that comes along with the air.
Solution: clean the slip ring inside the IAC The IAC is a metal can beneath the intake manifold, with two 1" hoses that feed extra intake air around the throttle body to control idle RPM, and reacts to loads like A/C or heavy electrical (alternator) loads. The "valve" has three pins, the center is a constant 12V supply, and the outside pins are pulsed by the ECM to ground, to either open or close a circular shutter -- looks something like a revolving door. (Except mind would only open, and close halfway.)
Electrical Diagnostics:
Start the engine.
Disconnect quick connector at air control valve.
Test for battery voltage on the middle pin (it is pin number 2 "GREEN wire" if you slide the rubber off), you should detect 12V or so (with engine running).
Turn off the engine.
Test for ohms on IAC between middle pin and any side ones, you should have between 6 and 20 ohms in each case depending on the model. If you do have this resistance, then it means that the motor of the IAC is good. If not, don't give up yet.
Disconnect the hoses from the manifold and the intake hose, disconnect the 3-pin electrical connector, loosen the top nut on the band clamp around the valve body, then remove the valve. Off the car, look down the bore of the valve, and then by supplying the center pin with 12V and shorting either of the outside pins to ground, the "door" should fully open or fully close.
Disassembling and Cleaning the Valve
Clean the slip ring (the one wherein the brushes are touching) inside the IAC by taking the IAC apart. [Editor's note: this is not possible on newer IACs with no housing clips.)
Before you take it apart, mark the housing (a pen mark or screwdriver will do) so you can assemble it in the same position. IT IS IMPORTANT!
With a small screwdriver pry up the clips or crimps which are holding the housing (there are four of them). Once they are up, pry on the housing a bit and the whole thing should come out. At this point, you will encounter a bit of resistance because of the strong magnet inside, but there is nothing to worry about, just keep going until everything comes out. Be careful not to lose the o-ring or the small cone piece -- which will probably fall off the armature shaft and be laying at the bottom of the barrel with the permanent magnets and the wiper contacts. You MUST NOT try to push it in once you started separating the housing (or you will destroy the brushes inside the valve). Once you open it, you will understand why.
You will then see oil and crud all over the armature and the commutator. Clean it up with brake cleaner and carefully flush away all crud especially from gaps in commutator.
Clean the contact points with very fine emery cloth or a Scotchbrite pad and polish them. Be careful; don't bend anything. Again, make sure you don't lose the little cone piece. You'll need to get it out of the barrel for re-assembly - it will come out easily but you have to use something non-metallic because of the strong magnets around the housing.
When everything is spotless and oil free, put the cone on the end of the armature shaft, so that it tapers away from the armature. The cone is important, because it acts as a ramp when you replace the armature, gradually spreading the wipers so they land on the commutator without bending them out of contact. Also, a little silicone grease on the o-ring seal can't hurt. Once you take it out, slide it over the shaft and keep it in the upward position (so it won't fall off) while assembling it.
To re-assemble, put the tee upside-down on the workbench, with the cone in place, and gradually feed the barrel down. It's a bit of a trick to keep it straight, because the permanent magnets have a habit of sucking the armature from side-to-side. It doesn't take much force. Once the armature is seated properly, re-align the marks on the barrel and tee by simply twisting the tee relative to the barrel. If you forget this step, the valve may likely not open or close fully. After doing so, then you are done. Push back the clips (if you have clips, and don't use a hammer)
Re-test the valve as above with test leads before the final crimping. Mine worked fine now, fully open, fully closed. I then squeezed the crimp tabs back into place with large channelock-type pliers, and double-checked the alignment marks. Replace the valve, making sure the flow arrow on the tee points in the proper direction. The arrow should point TO the intake, FROM the main throttle inlet hose. Tighten the hose clamps, and viola! "New" IAC valve. The entire procedure, including the pulling of the valve out and installing it back takes about 30--45 minutes. Test the side pins for ohms and re-install the IAC. You should now have a fast idle. Oh, make sure your PRM at idle is about 800 rpm. PS: I drilled and put in a small screw to prevent housing from rotating.
[Another Tale of IAC Repair:] The following Idle Air Control Valve repair might be of interest to fellow tightwads who experience a HIGH idle problem. I removed the bad IAC. The valve was not frozen, but moved quite easily back and forth. That's when I decided to open it up and look inside. Opening involved prying open several tabs around the unit's waist. Out came the solenoid innards which looks like the armature of a small motor with enamel wire winding around three arms. The cap removed from the valve contains a magnetic lining along the wall and three brush contacts near the top. The top of the armature where the brushes should contact was VERY greasy. I cleaned that and the contact brushes inside the IAC cap. A multimeter confirmed that there was continuity among all three arms of the armature: ohms1to2=21, ohms2to3=21, ohms1to3=42. So apart from the grease, I could see no problems. Therefore, I put the armature back in the IAC cap. This required some trial and error because the armature keeps wanting to stick to the magnetic sides of the cap. Once back together, I bent the holding tabs back in place (keeping pressure between the two parts).
The first time I started the car after installing the cleaned IAC, the idle was still high. However, I removed the IAC again, wiggled the valve back and forth a few times, and reinstalled the IAC. I checked the resistances at the electrical connection pins and th
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