Hi,

My daughter and her 89 244 auto are in the neighborhood. She has a summer job teaching ESL at a college about an hour away and it's given me a chance to explore a low idle and occasional stall at red lights that she's complained about for a couple of years.

I mailed her a used TPS when this first came up. It seemed to bench test ok, but it did not cure the fault. I had the car for a couple of hours yesterday and would like to know if I'm on the right track.

I don't have a tach, but the idle is indeed low. Neither does it produce a momentary high idle at start up. As per Bentley, I checked for continuity between pin 2 at the ECU and ground with the key out. It was inconsistent. I also disconnected the IAC at idle and there was no change in RPM.

Both of the spare switches in my junk box would click, but only showed continuity on the bench if I applied pressure against the stop with my fingers, so I set them aside and removed the TPS from my 91 that idles normally.

Putting it into her car, I now had consistent continuity at the ECU and the idle came up a bit, close to normal, but there was still the lack of momentary high idle. Disconnecting the IAC with the car running now produced a high idle, I'd guess 1000 RPM or so, and swapping the IAC from the 91 produced the same effect. Am I right in thinking the IAC is open when disconnected and it only limits the idle air when it's working ?

The car will return next week-end and I'm wondering if I should have been checking for voltage at pin 2 of the ECU with key on. It seems I've read something about that but can't find it on a search.

I'm also wondering if a the normal high idle at start up is temperature dependent making the temp sensor a suspect. Or perhaps the ECU itself, a white label 561 is misbehaving. The car is well tuned. TB is clean and it runs beautifully otherwise.

There's not much that I can find on low idle searching the BrickBoard other than an ancient post by Lucid about an experienced Swedish Volvo mechanic he knew who claimed that deposits on the intake valves can suck up extra fuel introduced at start up and negate it's effect. It's an interesting hypothesis because my daughter uses her car mainly on short trip city driving, although coming off a 3000 mile highway cruise, I'd expect the engine to be cleaned up.

Looking up TPS availability on Ebay, there's not a lot of options other that Bosch at $115. or Standard Motor Products around $50., but I was curious about this listing.

https://www.ebay.com/itm/BOSCH-0280120301-Throttle-position-sensor-for-BMW-M3-PORSCHE-VOLVO-JAGUAR-OPEL/233302074573?epid=79336336&hash=item3651e324cd:g:-WwAAOSwOgFc24Q-

This is the first I've seen of the innards of the beast. For whatever reason, I'd always thought the box was in-penetrate-able like the box that holds the vehicle speed connectors. No so, apparently. Has any one done this successfully ? Did I miss it somewhere on the BB ? I may see if I can't rehab some of my lazy units.

regards, Peter

Hi,

It’s interesting that you moved both the TPS and the IAC over from the 1991, to the daughters car and nothing changed?
I do not think this is a coolant temperature issue if it runs fine otherwise.
You can that at the ECU also. I think it’s pin 21 or something like that?

I looked up a reference chart, I found some time ago, that shows outs of changes with the ECU’s just after the 1989 year.
Look here and see.
http://www.nuceng.ca/bill/volvo/database/ecu.htm

It makes a comment about the 561 in boxes below that move up in years. So just thinking you might be on to an issue that occurs with the 561 from time to time.

Like Pageda says, the TPS either work or they don’t, if they are set right. An ohmmeter must show it operating with the throttle closed and then open. We don’t care which way it goes, just as long as it changes an state, to its opposite reading. Same for the wide open throttle position.
It should be telling the ECU to go from idle to Powering up mode or Wide Open Throttle mode.
The idle is guided by rpms inside the EZK system.

The TPS gives the ECU a heads up that the, driver, is changing air flow quickly! The ECU is fast to shift things but there are other things involved, that that are not going to report it, too it, in time.
That’s why there is the TPS to give it the extra heads up that shifts the programs to drive on.
As he says the TPS has to be set on the hairs edge of the throttle plate wiggling open from being absolutely shut down.
This is where the stop screw gets over used incorrectly. It’s not an idle screw but a STOP screw to prevent the return spring from possibly over jamming the throttle plate closed in the bore,
in case of a fall from WOT.

If you are not having the idle “jump up” upon starting, with you foot completely off the gas pedal, it’s not doing like it’s supposed too!
The IAC has to have complete control.
The TB has to be set within its range and not higher! Apparently you are low enough that you need an operating IAC or a signal to the ECU or it must need to respond back to the IAC.

I’m afraid that you are onto “A” harness issue to the TPS or the ECU has gone consistently flaky!
You can read up on the “intermittent stalling” issue here on the same year but 700’s.

https://www.volvoclub.org.uk/faq/EngineFIComputer.html#Intermittent_Stalling_Bad_ECU

You will have to scroll around a little but it’s interesting!

Good luck
I hope this helps!

Edit: I should look before I post! Art was here, just like Mighty Mouse! (:) he saves the day!

Phil

Hi Phil. Just a side note. Even though the TPS electrically provides a WOT position signal, to the best of my knowledge it is not used by any of the Bosch LH 2.4/2.2/2.1 fuel injection ECUs or the EZK ignitions systems, but is apparently used by the Regina systems, although I'm not sure of the details. As I recall, I was able to verify this in the Volvo electrical manual ECU wiring diagrams.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi Dave,
Thanks for the love touch on the shoulder.

Its ok not to know everything just know it’s built into the switch.

I guess you can be the next person that Art can “pull up on ... our boot straps” with those kind of details.

I have only read that the signal is suppose to shift the mixture more rich and hold the timing advanced unless it gets a knock sensor signal.
They put it there for some purpose on some engine, be it ours or not, is my only explanation.

Arts our guru, as I think, he has been into some dark places on these cars, to where he gets back out of there using the flashlight on his camera!
(:)

Phil

"Arts our guru, as I think, he has been into some dark places on these cars, to where he gets back out of there using the flashlight on his camera!"

Oh so true and I'm always prepared to be pulled up by my bootstraps whenever I make such posts, especially in the 240 forum.

As for WOT, I recall a discussion many eons ago about WOT here when someone mentioned their OBD system wouldn't give the 3-3-3 code for WOT in Diagnostic Test Mode 2 on an LH system and wondering if their TPS was faulty. I think it was one of the Volvo Vista Master Techs who used to lurk here making the comment that WOT was only used by Regina systems at that time. Surprised, I went out and verified that DTM 2 did not respond to WOT on my own LH 2.4 car at the time. I vaguely even recall finding that the WOT signal went to the ECU connector, but when I tried tracing it onto an ECU board I had hanging around, it went nowhere. Yet I now see a mention on TBricks of WOT in LH 2.4 causing a different fuel map to be used. Hmmm, I imagine I'll soon be learning more about this.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

The contacts for wide open throttle are those that are exposed -- seen in the upper left of that ebay picture.

Once, Dave, I imagined as you, that WOT was not used. I'd done as you too, attempting to get the sensor test response from OBD (mode 2) for wide open, which one would do from under the hood by grabbing the spool and twisting it.

I even swapped the TPS with a spare I had just verified with an ohmmeter, getting the same result -- no WOT contact closure. Scratched my head. My first hypothesis was the throttle spool limited travel, and that's why I couldn't get the good switch to close.

My mistake was not twisting the spool hard enough to actually open the throttle completely. There is a step in the spring response just before the switch engages, as the kickdown cable on our automatics does its business, which you can overcome almost without feeling it using a heavy boot on the accelerator pedal, but requires conscious effort to effect at the spool by hand.

WOT signal is indeed sensed at the fuel ecu and used in the subject vehicle.
--
Art Benstein near Baltimore

Never test the depth of the water with both feet.

"As he says the TPS has to be set on the hairs edge of the throttle plate wiggling open from being absolutely shut down. "

This advice, Phil, is what I believe contributes to the flaky operation of the TPS, when it is taken literally. If you examine the operation of a snap action switch in close detail, you'll find that the snap, or click, is not the entirety of its conversion of motion to electrical function. You'll find the switch is even sloppier in this as it ages.

This is noted by Peter when he bench tests the switches and find he has to add just a little extra pressure to get the switch to close after the snap. You can test this too, with a spare switch on the bench. If you operate the switch in very slow motion, thou by thou, so to speak, you will see that setting the switch on the "hairs edge" will just get you in trouble. Add temperature variations to this and the trouble will be worse.

The idea of getting the switch to open at the slightest press of the go pedal sounds good to us as boy racer off the line performance. I'd be more concerned that the idle control is brought into play in every case when the pedal is released than taken out of play at the slightest touch.

So, yes, adjust it so it clicks when the throttle is closed, but set it so it clicks even just a tiny bit before the throttle is tightly closed. If this is confusing, use an LED test light on the circuit to prove that it indeed goes out (switch closes) every time the throttle is released.
--
Art Benstein near Baltimore

Always remember that you're unique. Just like everyone else.

Hi Art,

Just read your post and I guess you are right about what is considered a “hairs edge” to many people.

I will have to say, that when I’m taken literally, I can get taken out with the trash! (:)

The whole thing I was trying to instill was the fact to tell the ECU to advance into the next program appropriately.
One has to keep the idle speed being controlled on the IAC.
The throttle plate can easily raise idle speed due to the surface area of circumference space.
You don’t want the plate open Too much and then have the switch turn state as you will be running in a mixture deficit and have stalling or higher idling issues just from that.
Barely cracking the throttle open will rapidly allow enough an inrush of air flow to instantly change the vacuum in the manifold plenum.
One has to remember that it was under an ideal lean idle mixture of control, to control emissions, to the set mandates.
The idle rpms are watched closely to reduce fuel consumption for the ratings system. Finally putting money into the high number of gears in the transmission instead of tricks.
Now they are going as far as disabling various cylinders or the whole engine.
Now that’s got to be a headache, maintenance wise, in short order.
With new cars you get ponder the difference between a maintenance gouge or being gorged up by the blue book resale depreciation!

The ECU program will be raising the injector mixture on the TPS command Long before the O2 Sensor responds. The AMM is oblivious to the oncoming change as well.

For my cars I admit I do stress on that a wee bit. It’s better than emitting! (:)
On some models this shift in program brings on the EGR function at some point? I think it does this in later RPM’s or at a road speed, so it affects the plenum less.
A sticking EGR, either opening or closing off completely can cause a drivability or CEL issue.

The East coast cars have less of those running around but we get to have less cars with rust issues.
Since you have more green trees and bushes, you have more “air cleaners” standing or lying around!
It must work because, at my Northern ocean home, my used cars are exempt from smog certification excepted when first purchased. Several counties are blessed that way luckily.
I stress on myself again to keep a car tuned up despite this.
It’s easier on starters and the fuel wallet. California fuel runs about a dollar or more a gallon, than the East Coast side, due to the taxation straw sucking in there!
My small California Northern community pays even more!
It’s like what Hawaii pays, due to supposedly mountainous roads and being small. It drops back $.50 within in California a 150 miles away, but Hawaii is 2,000 miles away over the ocean. Go figure as I do distributor greed.
I fill up in Oregon when ever I can. Thank heavens for interstate commerce laws.

Anyway Art, you are right on, as usual!
Good to see your hanging out and being a watchdog for us!

Phil

I have found low unstable idle and stalling to be related to dirty throttle body. So thoroughly clean the TB, idle air control valve, and PCV system. Make sure all vacuum hoses and fittings are open a freely passing air.

Also make sure the TPS is adjusted correctly. The TPS is just an on / off switch so it either is working or not.

Dan

"The TPS is just an on / off switch so it either is working or not."

Indeed it is just a switch -- a snap-action switch for which Microswitch (Freeport, IL) made its name. Problem is, it can be working one second and not the next, and then work again. Intermittent. Inconsistent was the word Peter used, I think. This is due to oil getting inside and eventually burning between the tiny contacts, in my theory.

Because it only switches logic levels, there's not enough current to burn through consistently, and like any low voltage connector, it eventually gets flaky.

Monitoring the voltage is exactly how I proved this trouble. I used an oscilloscope with a stable connection to the ECU pin, so I could watch for consistent switch closure as I tapped the accelerator pedal with a toe. A multimeter watching voltage would be less telling, because of the time for digital meters to settle and stop flashing digits, but could do better than an ohmmeter at identifying a dirty switch.

I don't know that the "initial high idle" is really a thing. I've heard Phil mention it on the board, but I don't recall any of my (non-EGR) cars ever doing such a thing, even in Winter. Maybe I'm not paying attention?

two types of tps

One switch is sealed, and another can be opened.

--
Art Benstein near Baltimore

"Carefully pry (If this were a Jaguar you would prise)..." -BrickDad

Art, do you recommend attempting to clean a dirty TPS contact area? I know many people recommend against it, but when I've had a flaky TPS out of a car that has been exposed to a lot of grungy throttle body build up, I've never been afraid to briefly soak it and shake it repeatedly in solvent or spray contact cleaner in an attempt to dissolve/dislodge some of the internal grunge around the contacts as long as I immediately shake it out and air dry it. Never had a problem doing this myself and never had to replace a worn TPS. For proper TB adjustment, Volvo has rather exact specs, which vary a bit by engine, for setting the throttle plate stop screw, adjusting the TPS with a thickness gauge at the throttle stop screw and then adjusting the linkage rod to the throttle spindle stop and finally the kick down cable free play. I had it all published in the 700/900 FAQ at one point, but it has seemingly since disappeared.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

If you're certain you have a TPS that's messing up, giving it a bath seems like a good alternative to placing an order. I never dreamed these things would become as expensive or hard to find as this thread implies.

Just to be sure, I checked one of the spares I have to see if I could open the snap-together housing and get closer to the Microswitch inside. In addition to the snaps, I found a bead of hard (epoxy?) sealing the two halves together, and in deference to the value these things have apparently acquired, declined to risk its destruction. I don't have a switch deemed "bad" or I'd bust it apart just for the pics.

As for adjustment, I believe the feeler gauge at the stop screw should be sufficient to keep even a worn switch from landing on the hairy edge at closed throttle. Usually this is compounded by deposits on the throttle plate and wear in the shaft as the car ages well beyond the service life anticipated by the techs who wrote up those green service manuals before even the first of them appeared on the market.

Philosophy, rather than recipe, should be that you want the idle to be regulated when your foot is off of the pedal, and switched out of regulation before the throttle opens wide enough to inch you forward in a hot traffic jam. Yet I understand the need for recipes.
--
Art Benstein near Baltimore

If you think nobody cares if you're alive, try missing a couple of car payments.