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I'm looking for new suggestions to a frustrating problem. For over a year now my '91 has been stalling at stops (and idle), slow speeds in intersections, and any time the gas is released quickly. I've read old posts and tried most of the suggestions. I've put in a new IAC, a new TPS, air filter, I even took apart and cleaned the throttle body. I don't think it's related to a fuel pump or fuel line pressure because I would think the issue could occur at any speed, not slow or idle. I have become extremely frustrated and it poses a safety issue as it stalls in traffic.

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When you changed out the IAC did you clean the oriface that it goes into? This might sound strange but did you check the ECM. Try replacing it with one that you know that works.Same goes for the coil pak and ignition module. The afore mentioned parts can cause the strangest problems. I had what I thought was a transmission problem, turned out to be a coil pak. My friend's 3800 would not start in the cold, tried everything, changed coil pak, problem gone. You should have a spare coil pak and ignition module anyway. Good luck.

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Does it just die or does it seem to stumble then die? If it stumbles then dies i would suspect the EGR valve is stuck open. If you can get it to stay running for a few seconds (hopefully running badly) try tapping the base of the EGR. If it starts running better the EGR needs to be replaced. You could try cleaning it but i personally have never had any luck cleaning them. Good luck and i hope this helps.

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I have read that the fuel line pressure could be the issue, but if the pressure is low, wouldn't there be other problems even at higher speeds? I've never dealt w/ an EGR valve. I'll have to research the location and replacement of it. So, next week I will probably tackle the coil pack, EGR, and fuel pressure. I don't know if it's related, but my dash also displays 00 error almost every morning. I've had that problem before and cleaned the connections under the sterring column. After it's first trip from home to where ever, it works the rest of the day.

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Also, it does stumble, then die. The RPM's drop low, shoot up over 1000, drop again. At idle or stopped this repeats a couple times then stalls. At low speeds (i.e. starting into an intersection or quick release of the accelerator) it stalls immediately.

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Without knowing the overall condition of the engine components, and what has already been replaced, it is very difficult to attempt to fix a problem long distance.

The 3800 GM engine is a very common engine and any decent mechanic should be able to analize and fix the problem. Also with a shop manual and a little time you could go through the ECM diagnostics and verify that everything is within spec.

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Does sound like a classic "sticking IAC" problem but one question: does this happen when cold (approximately the first two minutes after starting) or only after in closed loop operation? Until in closed loop the O2 sensor reading is not used by the ECM.

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When I purchased my '90 convert it had a dying problem. It turned out that its air conditioner had been converted to R134 and had been over charged. The knowledgeable GM mechanic I took it to said it was not an unusual occurance.

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Padgett- It stalls any time, from 1st start up of the day or any time during a 20 min drive to work. In a nutshell, the factors I'll be narrowing down this week are between the ECM, EGR, coil pack, ignition module, fuel pressure, vacuum lines, and the O2 sensors. Good thing I've got some days off! Thanks for all the suggestions, I'll let everyone know how things turn out.

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O2 and EGR only come on line when in closed loop operation. If problem occurs at startup (during open loop) you can eliminate them. Certainly you want to check other things but if it runs well when your foot is pushing the accellerator and erratic/dies when not, that is classic IAC. Just about anything else will make the idle low or high but overshoots in both directions are almost always the IAC.

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Well, I didn't get to work on the car this past week, so I'll have my work cut out for me next week. Any way, one thing I forgot to mention, is that the exhaust seems to have a "rich" smell to it. Could that be related to my stalling and/or starting problem also?

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Padgett, you said the problem sounds like a classic sticking IAC. I've replaced the IAC twice in the last 3 months and cleaned the throttle body, including the housing for the IAC. If it is the IAC, what else could cause it to stick? Thanks.

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Bad wiring to the IAC ? Failing IAC driver in the ECM ? Bad tach signal from the Ignition module (should see on instrument panel). If runs well when foot is on gas, it almost has to be the IAC or a stuck open EGR (but EGR will not cause high rpm excusions)

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After reading up on the the function of the EGR valve and the symptoms a bad one causes, I'd have to agree w/ Padgett on a bad EGR. I reviewed the '91 engine documents, but I haven't been able to locate the EGR. Can anyone point me in the right direction or refer me to the correct location in the service manual? Thanks.

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Padgett,I posted this on another topic but you apparently did not see it.

In your article in cleaning the IAC you said not to turn/adjust it. I fiddled wiht it BEFORE I read your excellent article & now my '89 stalls only on initial start up unless I give it a little gas. It usually only does this once on initial start up, but is annoying. Is there a spec to adjust (re-adjust) the IAC? I couldn't find one in the manual.

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If it runs at higher rpms, but dies at idle check out the cam position sensor. Mine would stumble and carry on at idle and die if left idle a bit, but as long as I gave it a bit of gas it would level out and run smoother. It also felt hesitant when accelerating. Think Padgett had a post on JB welding it. Hope that helps.

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Maybe you have a "Going Problem" instead.

There's the cam sensor itself, and then inside, there's the interruptor that Padgett described fixing at his site, www.6007.us. I was thinking, however, that if the cam sensor or interruptor was faulty, there'd be a CEL.

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CEL can be tricky though. An example is when my crankshaft position sensor went bad. The car wouldn't start at all, but no error codes were thrown.

The Maui convertible we had had a code EO41, which was from a bad interruptor magnet. The car started and ran, but I'd say at about 80% power. I guess in this situation, my camshaft position sensor wasn't getting a signal from its magnet, so the sensor wasn't sending a signal to the engine computer, which improvised. The factory service manual says that the engine computer will pick "any old" plug to fire (or is it injector) with a 1-6 chance that it's right.

At any rate, I'm thinking that the camshaft position sensor isn't your issue.

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Could the crankshaft position sensor be partially bad? I know for sure that it needs to be working to start the car, but may be intermittant. What I don't know, is if the engine would die if the signal is lost while it's running.

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AFAIR (is in the FSM), driving over 38 mph for a few minutes will reset the IAC.

BTW a bad cam sensor will set an error code 41 but a bad crank sensor won't (because usually the engine won't start). Secondary ignition will not set a code either.

When the cam sesnsor goes, the engine will usually run (two opposing plugs fire at the same time so being 180 out does not matter) but the injectors fire in parallel instead of sequentially - if the pressure in the fuel rail is at all low, the engine will run lean and not be able to correct.

Have seen crank sensors with part of one of the three magnets broken off. No telling what it will do then.

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I changed my harmonic balancer this past March and at the time the sensors and magnets appeared to be in good shape. The car has been stalling for about a year now. Above anything else, I don't want to have to remove that balancer again to get to the sensors. I'll change everything else before I pull that apart again.

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  • 4 weeks later...

Add my name to the list, My car starts as long as I lay my foot on the gas pedal to open up the throttle valve (2000 rpm) when it falls below that the idle is rough and when I remove my foot, it flips over and does the dying cockroach. I will be going through this thread to resolve my issues. I will apprise my fellow experts of my progress.

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I have not checked the fuel pressure yet for two reasons:

First off, Autozone doesn't rent the pressure tester any more, they only sell it.

Second, I've had this problem for over a year and a half and if my pump was going bad, it should've gotten there by now. I may possibly get the pressure tester just for the hell of it next week when I take a crack at replacing the vacuum lines. I'll let everyone know if I reap any benefits from that.

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While attempting to cure another problem, I created a problem last week by "improperly installing the IAC" <img src="http://forums.aaca.org/images/graemlins/shocked.gif" alt="" />. If cocked when installing or not properly seating the IAC, it is easily possible to deform - pinch the O Ring causing a leak. While resolving the problem I also noticed that it is also possible to install the O Ring in the wrong location on the IAC .... Just trying to help - You might want to re check your IAC.

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> Maybe you have a going problem.

</div></div>

<img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" /> <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" /> <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" /> <img src="http://forums.aaca.org/images/graemlins/blush.gif" alt="" /> <img src="http://forums.aaca.org/images/graemlins/laugh.gif" alt="" /> <img src="http://forums.aaca.org/images/graemlins/laugh.gif" alt="" /> <img src="http://forums.aaca.org/images/graemlins/laugh.gif" alt="" />

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