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I've cleaned out the following on my car, and have a resulting (and common) problem with a high idle .
- Throttle-Body
- Aligned Throttle-Body butterfly valve so it closed snugly. Needed to do this as I had to remove the shaft for lubrication.
- Set the idle stop on the throttle-body to spec (1/2 additonal turn after it just touches the trottle lever)
- Installed a new TPS and set it AFTER setting the Idle-Stop. Verified TPS works fine
- Fuel-Injectors
- IAC. Opens and closes perfectly with an audible snap. Verified that valve works by blowing into it in both open and closed positions.
- Checked the AMM
- Verified O2 sensor voltage-range was healthy (0.2 -> 0.9v)
- Flame-Trap
- All hoses
After putting it together again, the idle jumped to 1500 - even with the black idle-control knob on the trottle-body fully closed. Allowed sufficient time for computer to get used to the cleaned components (just in case ?), but idle still high. I am nervous about high idles because of my delicate ZFHP22 tranny. I expected that grounding the White/Red test-point would 'CLOSE' the IAC and drop the idle so it could be solely controlled by the idle-setting knob - but it seems to do absolutely nothing.
At that point I cleaned the injectors and lubricated the seals (with ATF). Idle dropped down to between 800-1200 which I still consider too high.
Suspecting that the butterfly valve in the throttle-body was not fully closed (I can see a fine circle of light between the edges of the plate and the throttle-body - sort of like a very-fine corona in a total-eclipse) I decided to check how much of the high-idle was caused by this. I...
- Disconnected the 2 IAC wires at the big engine-wiring-harness grey-conector on the passenger-side, and temporarily shorted the white/red one coming from the IAC to ground - which fully closes the IAC
- Also made sure the black idle-control knob on the trottle-body was fully closed - which it was.
In this position, all of the idle would be controlled by air passing through the butterfly-valve. Was barely able to get the car started, and idle was around 150-300 with the engine threatening to stall at any time. Boy - that was the quietest I've ever heard a Volvo run !
So it was obvious the high idle was being caused primarily by the IAC. Which brings me to my main question.
During normal operation, does the IAC valve have just 2 positions: Fully-Open or Fully-Closed ? Or are there many levels between them ? And if so - how does the computer achieve these partially-open positions ? Is it by passing more current through the open-motor-widing than to the closed-winding ? Can this be easily checked by hooking up up a meter in parallel ?
How is the White/Red test lead supposed to work ? Is the change noticeable when grounding it ? Anyone know which terminal on the computer this goes to so I can short it at the computer itself avoiding a possible bad connection to the test-points...
Mine is an 85 740 Non-Turbo, so the only test-points are the idling & CO ones in the passenger-fender well. I noticed that there is a red-jumper wire connected at the LH Jetronics 2.2 computer box. Anyone know what this is for ? Can any codes be read from this point ?
Any responses would be much appreciated.
Thanks,
Noel
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Well – it finally looks like my high-idle problem has been solved. As I mentioned in my last post, I was beginning to suspect that though the IAS opened-fully and closed-shut just fine, maybe the commutator was dirty/worn in the partially-open area that is important for fine-tuning idle speed. The last time I’d cleaned it, I tried opening it by prying open the 4 pairs of claws – but could feel something holding it back when I pulled, so I ended up just cleaning the valve-section. That cleanup was sufficient to allow the valve-window to open and close fairly easily at the time.
This time around I decided to pull it apart firmly, as I’d read posts that indicated the resistance was on account of the magnets. With that in mind, I was able to pull it apart quite easily. The commutator had tracks on it form the brushes (which were more like a contact-terminal on a spring) but was not very dirty – which was surprising since the motor is not completely isolated from the valve-area of the IAC. Considering the valve-end gets so dirty you would expect some of that dirt to make it’s way down to the commutator. Odd it was designed this way…
It’s SO much more easy to clean the IAC when it’s opened up. I think it’s also better as you can direct the cleaner at all of the valve-section without worrying about it travelling down to the motor (which it will). When I removed the cir-clip which holds the motor-armature to the shaft (and which it spins on), I noticed that the shaft had gummed-up oil on it that was probably on account of the cleaner mixing with the oil and drying it out. After cleaning it out, oiling the shaft, polishing the commutator with fine sand-paper, and flexing the contact-springs in a bit more towards the commutator - I was ready for the final step that was supposed to be the most problematic: inserting the armature back in without bending the contact-springs while fighting with the magnets. At the end of the shaft – on the commutator, there is a thick tapered plastic-washer that acts as a ramp for the contact-springs to get onto the commutator. This makes the task very easy. The trick is to hold the armature tight and steady while inserting it into the IAC body. Was anti-climatic for me actually, because it worked first shot. Took about 10 secs to fit it in.
One VERY important thing to remember when re-assembling the IAC, is that there are two ways to position the valve-end (the section with the valve that is attached to the armature) into the IAC body. These 2 positions are 180 degrees apart. The correct way will allow each contact (there are 3) to only track on one commutator-section over it’s complete 60 degree swing (the commutator is broken up into 3 copper-wedges – each with it’s own contact brush). The wrong way would allow each contact to cover 2 commutator sections during it’s 60 degree travel which would confuse the heck out of the ECU and of course, play havoc with your idle. More seriously, at one point in it’s travel – the 3 contacts would bridge all 3 commutator sections causing a total short in the IAC that would most likely fry the ECU transistors. So – make sure you mark the 2 sections before opening it up or check the armature orientation w.r.t the contacts before installing.
SO – after installing the fully-serviced IAC I took one additional step before starting the engine: I unplugged the computer, and left it unpowered for an hour. I could have also disconnected a battery terminal, but the ECU was easier for me as I had the cover off. I did this after reading Abe Crombie’s post on ECU ‘memory’ (see link below).
http://brickboard.com/ARCHIVES/1998JUN/10001844.shtml
Granted mine is an 85-era ECU and he’s referring to a much-more recent one, but what the heck. I didn’t have anything to lose (I’d actually unplugged the ECU before fitting the IAC in so I didn’t even have to wait).
After starting her up the idle immediately rose to around 1500 and then settled to a nice 700. The black idle-bypass screw was all the way in (since my butterfly-valve doesn’t completely seal the TB and lets in a tiny-amount of air I thought I’d avoid the bypass when trying it). So did this powering-down of the ECU help reset any memory it may have had of settings resulting from previously clogged TB, IAC, injectors etc ? Dont know - but it's something I'll do after every major cleanup in the future.
I still have a problem where grounding the Base-Idle test point does not affect engine speed at all to allow me to adjust the Idle-Bypass screw. But I could get around that by closing the IAC manually while I use the bypass-screw (right ?)
Hope my idle stays low now. I’m thankful that my ECU seems to function fine, and most of all – thankful to all you helpful folks out there !
Next mini-project is setting the CO level. My current test LED-light on the CO point is always on. AMM resistance is about 380 ohms which I believe is correct. Will try setting this using my spare AMM and see if I can get it to blink. Anyone else have a problem setting their CO where the test LEDs never really blink ?
Thanks everyone !
Noel
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Very nice description of IAC cleaning. I could feel that magnet trying to unsteady the hand as you fit it together!
You pose a couple of questions:
1. Not being able to disengage the idle motor using the test point. Can you verify the harness is actually grounding ECU pin 12? This is actually the same circuit as the WOT switch on the TPS. Edit: pin 15? There's a discrepancy between the LH2.2 manual and later wiring diagrams. I expect it really should go to 15, as it does on the LH2.0.
2. Not being able to see O2 sensor transitions on the test point. Can you verify harness is actually connected to ECU pin 22? The circuitry is rather reliable and midpoint in the flow, i.e. if there was a problem with the logic flow, the ECU would not enter closed loop. But yes, others have reported this trouble on LH2.2 700 cars. I wonder why the color code for these two wires is so different from that on the 200 cars? Could the wires be reversed in function? Hint - backbrobe the AMM pot wire pin 6 with a voltmeter to use as reference while adjusting-- your goal is 50% switching of the 02 sensor, and thus the LED test point.
3. Memory? Not on LH2.2. No adapting, no storage after the key is turned off.
Nice work and good feedback, Noel.
--
Art Benstein near Baltimore
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Hi Art,
1. I've successfully traced the White/Red IAC test probe all the way to Pin 12. I then grounded it and also verified I was getting ground at that point n the ECU connector. Is there a component in the ECU connected to these pins that could blow ? Maybe a past owner tried plugging that pair of leads into something.. In any case - does grounding Pin 12 simply result in the IAC fully closing ? Because if that's the case, I could do it manually too...
2. Ditto with pin 22 going to the White/Green CO Test Point. Traced and tested it. However, will also try connected the LED at the ECU connector end to eliminate wiring as a culprit (must do this with Pin 12 too).
I dont think the wires are reversed though, because I am achieving ground on the CO test point to light up the LED - something that I dont think could be done with the ungrounded idle test-point.
Not sure what you mean by backprobing pin 6 on the AMM. Could you elaborate ?
3. So it must have been the fully-serviced IAC then !
Thanks again,
Noel
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Nothing should be able to damage either function on the ECU. Both are well protected-- the input on 12 for WOT and the output on 22 for the CO test point.
Easiest way to check the idle test point (red/white) would be using a voltmeter. Probe the point with ignition on, motor not running. Not running will be obvious in the next step. The voltage should be a logic high - like around 4.5V, maybe 5. That verifies your connection to the ECU. While reading it, rotate your brand-new throttle plate to wide-open. It should then drop to zero. That verifies your WOT on the throttle switch, not that you need to, but it is good to know there isn't some carbon soot inside the switch, dragging the voltage down.
The CO test point is a 511 ohm resistor to a transistor collector pulled up to +12V through 1.5K ohm. You should be able to follow the O2 sensor transitions with either a meter or an LED on that point. It doesn't source much, mostly sinks through that 511 ohm resistor. Pretty hard to damage that circuit with a short, although there isn't any high voltage protection, say, if someone were to wire up their ignition secondary to the connector-- but now I'm getting silly.
If the transistor was shorted, you could measure 511 ohms to ground from that test point with motor off, key out. If it was open, I doubt the LED would light.
You could probably light the LED, though rather dimly, from the idle test point.
Backprobe (peel back the boot and put the voltmeter probe in the back of the connector while it is connnected) the AMM for voltage on pin 6 - the yellow wire to the mixture pot. As you turn the pot from one end to the other the voltage will vary from 0 to about 2.7V. This is a good way to know where you are in the setting; much better than guessing, counting turns or pulling it off and measuring resistance.
--
Art Benstein near Baltimore
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I have been following this discussion with much interest. I am attempting to get my '89 760 idle set properly. The problem I have is that grouding the test point does nothing. I have cleaned the throttle body and IAC valve. Prior to this, the idle would occasionally drop so low that it would stall - usually when creeping along in traffic.
I have been playing with the IAC and trying to adjust the idle. Grounding the test point does nothing and adjusting the idle screw with the IAC in place seems useless. I tried the 'feel' test to see if the IAC is alternating between open and close, and could feel nothing which surprised me. I know it is working because if I disconnect it (engine off) it ends up in some random position and the engine idle is random upon restart. I took my stethascope and listened to the IAC and heard it humming, estimate 60 to 100 hZ. This is easiest to hear with the engine not running with key in position two. This isn't what I was expecting. I was hoping to hear the armature clicking stop to stop.
My theory at the moment is that the valve is not opening and closing at this speed, as it is not likely it could oscilate that fast and would make a louder racket. I believe that maybe one coil is fully grounded and the other is being pulsed with a varying duty cycle which presents an opposing magnetic force of a variable magnitude. This would give full 'analog' control to the position of the armature. (Could be both coils are receiving complimentary duty cycle pulses.)
I have been trying to collect bits and pieces defining the output pins of the ecu. (LH 2.2) This may allow me to verify the above 'theory' as I am not a big fan of piercing insulation of wires.
When I had the throttle body off for cleaning and adjustment, I forgot to verify that the idle position switch contacts are working. I have the click set as per the FAQ, I just don't know if the insides are working. I suspect that if the ecu must see "idle on" if it is going to close the IAC for base idle adjustment. Any comments? Note: I used my listening test as above with the engine off and the hum wes present without regard to the open/closed position of the throttle body and without regard to grounding the test point. I did not try WOT.
One additional note: In this car, the jumper is installed on the two pin "test" connector adjacent to the ecu. I pulled one from another car at the local Pick-n-pull and the jumper is not installed. Makes me wonder what is correct. I might just need to buy a box of donuts and visit my local mechanic one morning.
In the throttle body, I too can see a halo of light around the throttle plate when fully closed (stop screw fully retracted). Is this normal?
Thanks,
Dan
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<< adjusting the idle screw with the IAC in place seems useless >>
Is your idle-bypass screw (the black one) tightened all the way in ? I suspect it is, given your throttle-butterfly valve is not completeley seated like mine. In any case, you should be able to at least RAISE your idle with that screw by unscrewing it.
<< This isn't what I was expecting. I was hoping to hear the armature clicking stop to stop. >>
I too had expected that. Actually the 2 transistors controlling each of it’s 2 coils are able to keep it in one of countless positions between closed and fully-open.
<< I believe that maybe one coil is fully grounded and the other is being pulsed with a varying duty cycle which presents an opposing magnetic force of a variable magnitude >>
I don’t think it works this way. If it did, the maximum it could be controlled was from fully-closed (if the closing-coil was grounded) to half-way closed.
<< I am not a big fan of piercing insulation of wires >>
You don’t need to pierce wires. The way I check continuity is by either...
- probling the inside of the component-connectors after peeling back the rubber boot
- disconnecting the large grey connectors in the passenger-side of the engine, and probing the inside of them
and the best way...
- disconnecting the large ECU connector, loosening the single screw on it that allows you to open out the connector exposing the back of the terminals along with the pin-numbers – and then checking continuity to the TPS, IAC etc. This allows you to check whether the TPS is functioning (by opening and closing the throttle), check coil-resistance of the IAS, Temperature sensor etc. You also end up verifying that your wiring-harness is fine. And most important, you verify all of this as close to the ECU as you can get.
<< I suspect that if the ecu must see "idle on" if it is going to close the IAC for base idle adjustment >>
Not true. When I had the IAC rigged up so it was being run by the ECU but didn’t have rubber hoses attached, it didn’t swing closed if I opened the throttle. Even with throttle opened a lot, it took a while to creep into the closed position. And remember – it never really fully-closes in base-idle.
<< In the throttle body, I too can see a halo of light around the throttle plate when fully closed (stop screw fully retracted). Is this normal? >>
No – this is not normal. I ended up compensating for this by fully closing the idle-bypass screw. However, one thing you should note is that even with the throttle-stop screw fully removed, the butterfly-valve could still be held from fully closing by the stop in the TPS switch. That’s why it’s important when setting the idle-stop on the throttle-body to loosen the idle-stop screw, loosen the TPS (or better still – remove it) and THEN set the idle-stop screw. You then reconnect the TPS switch and adjust it’s position. You might find you don’t have a halo any longer.
Noel
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Thanks for the informative reply. You have added to my understanding which is always a good thing.
I haven't found the time/energy to trace out the wires from the ecu connector. Maybe it is time. Better yet, time to invest in the electrical manual for this car. I guess I'll have to get the scope out and look at the IAC signals after tracing the harness.
When I adjusted the throttle body, I followed the FAQ procedure to a T. I did loosen the switch to make sure it was not acting as a false stop for the butterfly valve. I set the stop screw only 1/4 turn beyond 'touch'. Then I adjusted the switch to click with 0.15 mm shim and to not click with 0.45 mm shim. There was a pretty thick ridge of varnish in the throttle body before cleaning. I used throttle body intake cleaner only, no tools or undue pressure to remove it. I suspect the thin 'halo' is the result of abrasion of the brass plate on the ridge of varnish. (???)
The base idle screw is not fully in, but as I said, if I adjust it with the engine running, the idle does not move noticably. I just figure that as I adjust the screw, the ecu conteracts by moving the IAC in the opposite direction. I'll try it by clamping the air hose and see if I can get a 'correct' result. I am convinced that the procedure of closing the IAC for setting the base idle is to make sure that the "home" position of the IAC is set to provide the most latitude for the ecu to keep the idle at 750+/-. I would assume that this is near the 1/2 way point of the IAC range, but that is not for certain.
Again, thanks for your response. If I learn something new, I'll post it here for all to share.
Dan
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Dan,
Noel is very thorough in understanding and explaining that valve. I agree, in thinking the base idle set operation of the idle valve does not shut it down, but sets the duty cycle at a fixed point, like you said, one that allows the widest range of correction by the ECU. Probably pretty close to a midpoint for flow.
Also, I believe its vibration does not have much amplitude. What I mean, is the mass of the armature and valve assembly don't allow for it to open or close very much in either of the two phases. So its operation may be infinitely variable between open and closed, but instead of drawing the huge currents an analog servo would require, the motion is done binary fashion with much less electricity and heat.
I do know the two coils are alternately grounded by the ecu pins 10 and 23. One always has the opposing polarity from the other. This in itself would make it reasonable to guess it never stands still as long as the main relay supplies current to the center terminal of the valve (and the ecu is working!), so I guess you may not see a change when you use the test point, under certain conditions.
My experience with LH2.0, which apparently uses a different test point to set base idle, on pin 15, is the idle may or may not change when you connect the ground to the test point, but it always jumps up and settles when the test point is released and feedback takes over. Can't claim any LH2.2 experience.
(It was decided the wife's 89 245 won those beautiful corners, btw.)
--
Art Benstein near Baltimore
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Thanks for the fedback Art. I agree with your complimentary comments regarding Noel's study and explanation. If we only had our hands on the ecu source code we could fully unlock the mysteries therin.
We are on the same page vis-a-vis the pulse frequency contrasted with the armature inertia keeping the amplitude down. Have you measured the duty cycle and pulse width of the two signals?
If grounding the test point, doesn't induce the ecu to hold the armature closed, is the alternate method of clampig the IAC hose shut to set base idle off base? (pun intended)
Thanks again to both you and Noel for sharing your knowledge and wisdom.
Dan
Regarding the corner lights, no surprise there. Hope you earned a brownie point or two.
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...maybe that method is in Steve's FAQ? I don't recall seeing it in any form other than a question.
But to answer yours, "If grounding the test point, doesn't induce the ecu to hold the armature closed, is the alternate method of clampig the IAC hose shut to set base idle off base?", I'd have to first verify what flow the base idle setting test point allows. Of course, if it is anything other than nothing, clamping the hose would be a poor alternate.
Yes, I've had a scope on the idle motor (LH2.0 and LH2.4), but I didn't take any serious measurements on the three wire version at the time. (years ago) I've managed to own a number of these cars without yet being able to blame the IAC for any of my troubles. I think your frequency estimate matches my memory - vibrated about like my pager does.
You are right about the source. I'd be interested to see it, though ordinarily I don't want to see any code after work. The black box approach presents more challenge; learn what it does and infer what it is supposed to do. It helps to share what's been learned so we can whittle away at those common mysteries.
--
Art Benstein near Baltimore
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posted by
someone claiming to be j
on
Wed Sep 22 09:34 CST 2004 [ RELATED]
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"Aligned Throttle-Body butterfly valve so it closed snugly. Needed to do this as I had to remove the shaft for lubrication."
Did you replace the seals? This area can be a source of unmetered air.
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The reason I opened the butterfly-valve in the first place, was because I found the TPS full of oil. Couldn't figure out where that came from. Oil can enter the TPS via the throttle shaft area - because it is not a snug fit (the TPS shaft-hole has slots in it). The TPS worked fine despite the oil - but I put a new one in after the cleaning.
I too expected there to be a rubber-seal on both ends of that shaft, but I found only one in the throttle-link area. The TPS end didn't have any. I have a spare throttle-body and that too dosn't have a seal on that end.
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posted by
someone claiming to be j
on
Wed Sep 22 07:38 CST 2004 [ RELATED]
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As a note, with IAC grounded you should be able to adjust idle to 650 with bypass-(donot adjust to 750 with bypass) when you undo IAC ground rpm should adjust to 750 by the ECU controlling IAC-
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Make sure the Throttle Position Switch electric connector is not exchanged with the IAC electrical connector.
The ECU modulates the IAC from full open to full closed. That's right, the IAC has an infinite number of positions between full open and full closed. There is a great description of this by Abe Crombie in the 700/900 FAQ.
--
john
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posted by
someone claiming to be art
on
Wed Sep 22 05:54 CST 2004 [ RELATED]
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John, I really wanted to read Abe Crombie's take on the IAC valve operation, but after half my lunch hour searching Steve's FAQs, gave up. Do you recall which page or section?
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Abe's original message is not in the archives, but I will post it here. All credit goes to Abe.
"A 1988 has a three wire idle valve where the center wire is powered via the fuel system relay and the two outer terminals are alternately grounded for a varying duration by the fuel control module. One terminal, when grounded, closes the valve and the other wire opens the valve. The percentages are reciprocals, i.e., if more air is needed to get idle higher the percentage of time grounded will decrease to 42% while the opening signal goes to 58%. High idle can be due to open or unplugged coolant temperature sensor, but this usually gives a rich mixture and poor running if this fault is causing high idle."
"A poor connection on the closing signal wire at idle valve could give high idle without poor running."
"If the wire connectors from the throttle switch and idle valve were disconnected at the same time it is possible to exchange them and end up with the connectors plugged to the wrong items. This can cause high idle."
"Unplugging the idle valve conector with it running on the car doesn't change the idle speed usually as that version of idle valve will simply stop at some opening and stay fixed at that position giving you an idle speed of between 700 and 2000 RPM."
--
john
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John, thanks for the email alerting me to your response. I think the thread has a lot of valuable info, so I'll add to it rather than directly reply.
Abe's explanation of something other than fully closed is called for when the base idle is adjusted meshes perfectly with my concept of how it ought to be designed, i.e., the idle computer would then have the ability to decrease the air as well as increase it from what is supplied by the bypass path.
But, that concept has some disturbing refutation in green manual suggestions I've seen quoted second-hand, where alternatively base idle is set with the hose pinched.
Now, more than ever, I have to go do an experiment on my LH2.0 car, using a dwell meter on the IAC signal, the base idle grounding, and a spare idle motor to view operation (see how much the valve is held open) with that signal supplied.
Abe also addresses the mixup possible with those two 3-pin plugs. I think it might be easy to damage the ECU (IAC driver transistor) if even momentarily run that way.
Thanks for finding that (however did you?) and posting.
--
Art Benstein near Baltimore
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"But, that concept has some disturbing refutation in green manual suggestions I've seen quoted second-hand, where alternatively base idle is set with the hose pinched."
My Green Books say to set the Basic Idle Speed by grounding the red-white wire of the test point. Pinching a hose works, but that is not the Green Book method.
"Abe also addresses the mixup possible with those two 3-pin plugs. I think it might be easy to damage the ECU (IAC driver transistor) if even momentarily run that way."
The ECU is not damaged by this exchange of wiring connectors. I know this from personal experience. Using identical wiring connectors is poor design on the part of Volvo and Bosch.
"Thanks for finding that (however did you?) and posting."
I used to print and save meritorious posts in three ring notebook binders. I found it there, and then went to the archives. It was not saved in the archives, so I quoted Abe since I couldn't provide a link.
I do wish Jarrod would do some programming so some of us could be moderators and put a Red Star on top quality posts.
--
john
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I thought they all were being saved now. Perhaps Mr. Crombie's post predated that and needed the Red Star approval to get into the disk.
>>The ECU is not damaged by this exchange of wiring connectors. I know this from personal experience.
Undoubtedly Mr. Murphy was working with you that day. When the connectors are swapped the transistor must sink a load well beyond its rated capacity, given the normal expected contact resistance of the TPS, the connector terminations, and the harness wiring resistance. Even the TPS contacts would suffer. Did it blow the LH fuse?
--
Art Benstein near Baltimore
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It happened many years ago, just when I re-installed the rebuilt motor in the wife.gov's 1986 745T. The car would start only when stone cold, and did not have the proper power. I sorted it out (before I found the brickboard), and it has run fine ever since. Except wife.gov overheated the engine badly, and I need to do the head gasket at a minimum.
I installed a Coolant Loss Sensor on her car about four years ago. The water pump gasket went, and she kept driving because the lighyt did not turn on. Yes, she smelled all of the hot antifreeze and saw the steam. But since the light was not on, away she went....
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john
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Gee, I thought I was the only one who lost water pump gaskets. Last time it happened I was driving, and even with the benefit of a turbo gauge plumbed into the cooling system (which helped the first time) it was only that familiar odor that caused me to focus on the gauges.
I decided I am an idiot and need an idiot light. A buzzer wouldn't hurt either; or like I've suggested for teen drivers, a set of relay contacts to disable the stereo;-)
Did you post mortem the coolant float?
--
Art Benstein near Baltimore
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Not sure if this is the post John was referring to...
http://brickboard.com/ARCHIVES/1998JUN/10001844.shtml
By the way - anyone knows what that jumper-wire between pins 11 & 19 on the ECU 544 does ? Does this ECU allow you to see any error/diagnostic codes ? If so - how ?
Thanks,
Noel
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I don't think that was the post. That link referred to later adaptable ECUs, which started with LH2.4, I think. I dunno nothing 'bout Motronic, but obviously the EFI technology was more in code than hardware by then.
One thing that changed with LH2.4: the IAC motor became a spring-return, one direction motor (two wires), compared with the free movement, two coil motor in yours. The duty cycle is still used to control its average opening, but now the mass of its armature and spring determine the time to rest position.
I was hoping to see if Abe Crombie discussed the design (LH2.4) whereby its opening is by default a small amount, as if for a limp-around idle, should the control or motor fail. Applying voltage actually takes the valve through the fully closed position before reaching fully open. On the three-terminal idle valves, I'd guess yanking the connector would have the opening in a random position, possibly at 3000 rpm, hence the need for the ECU pin you short to mimic off-idle opening.
Pin 19 is a good question. In my LH2.0 cars it seems to be an undocumented MPU input, level converted with a transistor. The 83 manual does not show any harness jumper to ground, but the 84 diagram does.
On my sample -544 ECU, Pin 19 has the input protection parts installed (so you'll see the pull-up to 5V attempt if you disconnect it) but the level convertor transistor and associated parts are not installed on the board-- so it essentially does nothing.
Plausible explanation? Could be this is a relic of unheated 02 sensors, that being the major change made in 84 year to LH2.0? Perhaps this was a program jumper to indicate the use of a heated sensor, changing the warm-up map. I don't know. I can't find the documentation if it is there.
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Art Benstein near Baltimore
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More thorough tracing shows the -544 pin 19 signal is used. The unstuffed area is connected on through to T102 transistor, and then on to pin 37 of the MPU.
Still don't know what it is used for.
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Art Benstein near Baltimore
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I think you guys are on the right track, and Lucid and Art seem to have this down pretty good. I ran into an identical problem on an '87 240 Wagon back in June. The car started just fine, but no matter what I did, the ECU told the IAC Valve to go to full-open position. -and thus caused an idle surge to about 2500 RPMs as soon as the vehicle was started. I swapped the original 544 ECU with a spare 544 and a 511, but neither of them fixed the problem. I also seem to remember that the IAC and TPS were properly connected (not backwards), but the wiring harness was original and showing signs of rot.
Unfortunately, I didn't track the problem down. The car had been in an accident with a deer (most of the bodywork was already repaired), but the engine was knocking pretty hard from some unknown internal damage (possibly oil starvation). I ended up doing an engine swap, installed an OEM Volvo replacement harness (non-biodegradeable), and the problem went away. While I don't have a cut&dry solution to your problem, I'd would suspect that it's probably one of the 3 items:
1. Bad or damaged ECU. (it was ok in my case, but yours could be damaged)
2. Failing temp sensor. (somewhat unlikely for your specific symptoms)
3. Shorted wires in the original wiring harness. (possibly one of the IAC or TPS lines is getting shorted to a +12 or a ground wire inside the harness bundle when the engine is running)
4. Improperly adjusted throttle body that's allowing too much air past in the closed position. Either the Idle Bypass Screw (black thumbwheel) is not in correct position, or the butterfly valve is open a tiny bit.
5. Damaged IAC Valve (unlikely, but possible), I've had it happen on two vehicles.
I think you've pretty well worked your way through most of the potential issues. You're closing in on the culprit and I'm very interested to hear what the final problem is once you find it.
God bless,
Fitz Fitzgerald.
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'87 Blue 240 Wagon, 247k miles.
'88 Black 780, PRV-6, 145k miles.
FYI, the 511, 544, and 554 were the 3 ECUs that were used on the LH-Jetronic Vehicles from 1985-1988. All of them should be compatible/swappable, except for the possibility of an issue when using a 554 in a manual-trans vehicle (I need to do some more research on this one particular combination). The 554 unit was the final version and solves some of the minor lean-idle warmup mixture issues that were present on some of the 511 and 544 ECUs. However, a properly tuned vehicle using a 511 or a 544 will not have any noticable problems under most circumstances. See if you can borrow or pickup a 511 or 544 for about $10 somewhere. I can loan you one if you can't find one at a local salvage yard.
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>3. Shorted wires in the original wiring harness. (possibly one of the IAC or TPS lines is getting shorted to a +12 or a ground wire inside the harness bundle when the engine is running)
There's a good reason for the ECU to go poof! I'd have to give that strong consideration with wiring that looks like this:
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Art Benstein near Baltimore
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Thanks a bunch Fitz - for offering to loan me your ECU (mine is a 544). I’ll check the local yard first and see if I can pick one up. Whereabouts are you by the way ? I live in the bay-area of California.
I too had a bad engine-harness problem until I replaced it with a good one from the yard a couple of years ago. Around the time I cleaned the IAC, Throttle-Body, Injectors etc, I noticed that the wiring from the engine-harness-connector that was going into the car on the passenger side (to the ECU etc) was starting to degrade as well. I stripped all the outer black-insulation from the harness and insulated each wire all the way to the firewall. Also checked and make sure none of the wires were shorting each other.
Regaring the possible culprit:
1. Bad or damaged ECU: I’m trying to exclude all the other components first– so if all else fails this will probably be the only thing left. Hope not though..
2. Failing temp sensor: I checked this at the ECU connector end – so as to make sure there were no breaks/shorts along the way from the sensor. On a cold engine read about 2400 ohms, and on a hot one around 300.
3. Shorted IAC/TPS wires in the original wiring harness: Again, checked both the TPS as well as the IAC connections at the ECU connector end so as to factor in break/shorts along the way. Everything showed up fine, with no shorts along the way. Checked TPS open/close as well as IAC resistance.
4. Improperly adjusted throttle body: I too wanted to know how much of the high-idle was solely attributed to the butterfly-valve – so I removed the IAC and bridged the hoses coming to it with a solid pipe – so no air was coming in via the IAC line. I then fully closed the idle-bypass screw. Car barely started, and idled at around 300 and died very soon. To allow it to run, I had to loosen the idle-bypass screw almost all the way. Achieved an idle of around 600. So I don’t think this is a factor, considering the idle I am seeing is between 1000 to almost 2000 rpm. When I was doing the TB cleaning and had the idle-stop screw and TPS fully-removed, I noticed that the butterfly-valve didn’t completely seal shut. There was a very tiny sliver of light that made it’s way through along the sides. I could have filed the 2 spots on the butterfly-valve that were stopping it from completely sealing shut – but decided instead to compensate for this very-slightly open position by not tightening the idle-stop screw that extra 90 degrees when setting it.
5. Damaged IAC Valve: I checked the IAC by applying ground to close and then open terminals, and both worked fine. I even blew through the hoses in both positions to verify that it was closing & opening correctly. I was beginning to supect that maybe the commutator was worn in the areas that correspond to the partially-open position only (which is probably the position it spends most of it’s life in) – which was causing it to behave erratically when idling – but allow it to pass the fully-open and close tests just fine. Since I already had the IAC off and the IAC line to the manifold already blocked-off, I decided to test it with the engine idling to see how the ECU controlled the valve. Before starting the engine I manually closed the IAC. On startup, the IAC shutter-valve opened about 1/2 way. I touched the shutter-edge with a pen to see how strong the motor was – and it was pretty firm, and you could feel the motor-buzz. Over the next 30 seconds the shutter slowly went to about 7/8 closed, and then crawled back to the 3/4 closed position. Of course this had no effect on the idle-speed because it was offline and not controlling the intake-air. I then opened the throttle expecting the IAC to completely close, but it had no effect which was surprising.
On opening the IAC I didn’t find anything visibly wrong with the commutator. It was not gleaming– but not dirty or worn either. This was surprising given that the motor is not completely isolated from the valve-area of the IAC. Considering the valve-end gets so dirty you would expect some of that dirt to make it’s way down to the commutator. Was surprised it was designed this way though…
SO – Will clean the commutator & brushes, oil the shaft and install it back in tonight. I’m not too optimistic it will fix the problem, but let’s see. The idling with the IAC connected had actually got much worse this morning – it now idles at around 1800, and if you open and then close the throttle with a jerk, it drops to 700 and then immediately jumps back to 1800. Not good considering I have a ZFHP22 tranny attached… :(
One question: How would the engine behave smog-wise without the IAC attached, and with the 2 hoses blocked ? That’s how I’m currently driving it, and apart from a low idle of about 700, it seems to run fine. Anyone have an insight on how this would affect a smog-check on a dyno ?
Thanks again for all your inputs, and will let you know how things go.
Noel
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During normal operation, does the IAC valve have just 2 positions: Fully-Open or Fully-Closed ?
It pulses rapidly between open and closed. The average open time (nominally 50%) determines idle speed, with increases for cold running, AC on, etc. as needed.
How is the White/Red test lead supposed to work ?
It should cause the IAC to go fully closed, to allow throttle stop to be set for barely running. This is all described in the 700/900 FAQ. Your throttle stop may not be adjusted correctly if you didn't do the complete adjustment sequence.
On 240 LH 2.2, that test lead comes from the WOT signal input on the ECU. With the TPS set correctly, the ECU then sees both "Idle" and WOT, which I assume is interpreted as a diagnostic call to shut the IAC. If your test lead does nothing, suspect the TPS, it's adjustment, or wiring.
Did you remember to connect the TPS harness? I left mine off once and got similar high idle symptoms.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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If the pulse is that rapid, I guess you'll need an O.scope and wont see anything with a voltmeter :(
I've been through the entire sequence of setting the idle-speed. With throttle-body off..
- loosened the TPS screws so it could rotate freely
- loosened the stop-screw so it didn't touch the throttle-lever
- slowly tightened the screw until it just made contact with the throttle-lever
- Turned it another 45 deg. and locked it down
- Adjusted the TPS position until the switch opened as soon as the throttle was opened.
- Installed the throttle body and verified that the TPS switch was ON by checking with a meter at the harness-connector end. Idle still high.
Do you know where on the computer I will find the WOT unput signal ? And what function is served by the red-jumper I mentioned that was at the computer-connector ?
Thanks for the input ! My IAC opens and closes very well with an audible snap, and the valve is very clean. But given that the open/close sequence pulses so fast - the commutator would need to be in perfect order. Wonder if I should open that and check it up. I did try it when cleaning it out (4 pairs of tabs that needed to be levered out) - but it didn't seem to move when I pulled and since I didn't have a spare around didn't want to force it. Maybe the magnets were holding it in place ? Should it come out easily ?
Thanks for the responses !
Noel
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I've been through the entire sequence of setting the idle-speed. With throttle-body off..
Sorry, that's not the entire sequence for Idle Speed. Setting throttle stop and TPS is the first part. Next comes the running and use of the test lead to shut the IAC and adjust for 700 rpm with throttle bypass knob (I think I goofed before by saying adjust throttle stop). That is "Base Idle". When the ground is removed, the ECU speeds it up to 750±20.
I'm guessing this is outlined in the FAQ.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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The 'running and use of the test-lead' is the part of the setting that I'm stuck at actually. Since grounding achieves no difference in idle at all, I cant really set it to 750 since it's already way above that EVEN with the black base-idle screw all the way in. I would have expected grounding it would result in a fall below 750 with the idle-screw in, but that hasn't happened.
If I can locate the computer terminal where the this test-lead originates from, I will ground it there and see if that makes a difference.
Thanks,
Noel
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It's terminal 12 in the Bentley 240 manual for WOT (LH 2.2).
You might also want to check TPS idle contact from terminal 3, since the input to 12 is a straight wire (for the test), while the input to 3 depends on adjustment and contact closure.
You've adjusted the TPS, but I'm thinking an idle contact problem could be causing both the idle problem and the failure to close the IAC with the test lead.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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Thanks for the quick reply Bruce.
Decided to go to the car and trace all the important wires to the computer - should have waited for your email :) Anyway, traced the following.
Pin 3 - Orange - TPS Idle-switch terminal 1
Pin 25 - Brown - TPS Idle-switch terminal 2
Pin 10 - Grey/Red - IAC Terminal for closing IAC*
Pin 23 - Yellow/Red - IAC Terminal for opening IAC*
Pin 12 - White/Red - Test Point for setting Base-Idle
Pin 22 - White/Green - Test Point for setting CO
Pins 11 & 19 are shorted with a wire-jumper (anyone knows what this is about?)
I've now verified that the TPS-closed signal makes it all the way to the computer (there is 0 ohms resistance between pins 3 & 35 when throttle is at rest, and I lose continuity as soon as the accelerator is pressed).
Verified that IAC is in the circuit - 46 ohms resistance between pins 10 & 23
Verified that both test-points are connected to the computer without any breaks.
The only thing I still need to check is that the center-terminal on the IAC is receiving +12v. This wire does not originate at the computer but is probably connected to the ignition-switch.
I plan on opening up the computer next to see if I can spot any obvious signs of trouble there.
Thanks again,
Noel
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posted by
someone claiming to be j
on
Mon Sep 20 15:47 CST 2004 [ RELATED]
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voltage to IAC comes from Main (fuel pump) relay.
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Just checked center-terminal of IAC. Correct 12V being applied. Inspection of the computer is next on my list - unless someone suggests something else...
Thanks for all the responses,
Noel
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Only thing I can think of that has happened before: If you accidentally swap the two 3-terminal connectors between the IAC and the TPS, the armature winding in the IAC will tell the ECU closed and full throttle at once. The only significant message is closed throttle. That causes one of the transistors feeding the IAC motor on pins 10 and 23 to let some of its precious smoke out trying to light up the TPS switch contacts with 12V. I imagine it doesn't take too long either.
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Art Benstein near Baltimore
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Hi Art,
Yes - I expect that is a possibility. Though the IAS wire is a bit shorter than the TPS extension, so it would be a stretch, but still - it could happen.
Opened up the computer, hoping I would be able to spot the obvious burnt component - but that double-sided printed-board was as clean as the day it was made. I was really impressed with the condition, considering it was 20 years old. Found 4 large transistors (3 on a large heat-sink, and 1 by itself), along with 2 smaller ones. Considering the amperage of the IAC, I suspect 2 of those large transistors are used to power it. Difficult to test the transistors on-board with a meter, and the problem is not serious enough to warrant desoldering to test them - especially since I dont have a spare on hand. So I ended up putting it back together and reconnecting it.
I've made a simple circuit with 2 LEDs - one green and one red, that I'm going to connect in parallel with the IAC so I know whether it is receiving an open & close signal. Lets see what I find out tomorrow.
Interestingly enough, while searching the archives - I found a post by someone named Vroom (see link below) where s/he seems to have the same idling problem, and isolated it to one of those 2 transistors in the ECU. Fixed it with a replacement transistor. Would love to contact Vroom, but unfortunately dont find a mention of the name anywhere else, so...
http://brickboard.com/FAQ/700-900/EngineFIComputer.htm#RepairingYourOwnECU
Thanks again for all the responses,
Noel
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Noel, on the liklihood of your TPS and IAC plugs getting swapped-- well I figure you'd know for sure on that one if it happened.
Regardless, if vroom needed a new transistor, could be you do too. The LED test should tell you for sure; I know that it works because I had both the 10 and 23 signal monitored on a breakout box with LEDs for LH2.0 cars. The IAC is the same circuit.
On the 544 I have made a few notes, precious few as I have never owned any LH2.2 cars, only an ECU from one. The two transistors are arranged such that T301 drives pin 10 and the base of T302, which in turn drives pin 23. This ensures 180 degrees phase difference for the IAC motor armature.
The collectors are protected against reverse spikes with 4004 type diodes, and the base to emitter resistors are 330 and 100 ohms respectively, so your in-circuit forward bias tests with a DMM will be less clear than you might be used to, but still capable of seeing a short or wide open. A Simpson 260 on low ohms, which runs a bit more current through a junction, will see through those resistors like they are not there.
T301 is the lonesome one to the side; mine is an SGS type BDX77. I'd look at T302, but that is under the heat sink clip and I'd have to drill the rivets to see it. I'd bet it is the same type, TO-220 package NPN bipolar. If I needed one I'd use a TIP-120, because that is what I have in the drawer.
Key thing to remember is one transistor should always be in the opposite state as the other, and that the ECU uses a separate isolated ground (pin 25) for these and the injector outputs. I'm sure you want to know what killed the transistor before trying another ECU, if that is indeed what happened.
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Art Benstein near Baltimore
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Thanks for that really detailed post Art. That's exactly the info I was looking for from Vroom. Yes - I was trying to test the transistors using a Simpson meter too - and was seeing really low resistances on most of them - which was really odd.
One question - when replacing a transistor especially in this instance, where they are used as a pair, is there a need to use a matched pair ?
By the way - I did the LED test and both glowed all the time. Also - when I did a test with the IAC where I could actually see the IAC window open/close (I'd blocked off both IAC hoses prior to that - you can see more info via my post in the link below) - the IAC window was adjusting it's aperture okay - so it was not open all the way - indicating (I think) that the transistors are not blown.
http://www.brickboard.com/RWD/index.htm?id=855909
Will let you know if I find any changes after putting the fully-cleaned IAC back in.
Thanks,
Noel
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No need for a matched pair. Save that idea, though, for the alternator belts.
Yes, both LEDs glowed on my breakout box gadget, but really they were flickering alternately at a good rate. I haven't tried it, but I expect a dwell meter connected at either 10 or 23 would show you the net opening of the IAC valve. That might be a better troubleshooting approach than LEDs once you know (as in your case) the motor is actually doing its thing, which you should be able to tell by feeling the vibration.
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Art Benstein near Baltimore
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I'll try to answer some.
12volts is all the ICV sees. Full open or closed, no inbetween. I had to clean my ICV several times. Grounding out the wire, I believe this will only work prior to the car starting, not while running. The 85 has no code reader. When I cleaned my ICV, I just grounded out the center pin(off the car) and put 12volts to one of the outside pins. Thats how I found out I didnt clean it enough, it didnt fully open or close. I took it apart to finish the job.
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Actually the center pin needs +12V - not Ground. if you grounded the center pin and apply +12V to the outer pins, it will work - but only with one of the outer pins (I forget which one). The correct way to test it is +12V to center, and ground each of the outer ones.
Also - if the IAC is fully-opened during idle - the idle is very high as there's a very large volume of air that can pass through to the manifold. I tested this too. That's what leads me to suspect that the opening is controlled rather than being just fully opened or closed.
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