90 camaro RS 3.1 liter. rough idle always, can't idle when cold, (it just dies) no trouble codes are being thrown, I had a chevy dealership check it out, they ran diagnostics on it and found nothing wrong with any sensors, they say electically its in good standing, But the problems im experience appear to be caused by a bad sensor. any suggestions on what to check? no matter how crazy they may sound? know of anyone with the same problem, and how they delt with it? (the problem improves greatly when TPS is unplugged) but the mechanics say theres nothing wrong with it. is it possible the ECM just went stupid on me? any pointers would be greatly appreciated

 

There are several items to check. If it still has the original Multec injectors they should be replaced with some Bosch injectors. Not only do they clog the coils also short and cause problems.

The latest MEMCAL is AZTY. It supersedes the others for a 3.1l with auto tranny.

Also, check the wiring in and around the coil and distributor. There is a TSB that mentions (along with the MEMCAL change) it has a habit of chaffing and cutting through the insulation. This causes rough running and cutting out.

Last but not least, an idle learn is required after any time the battery power to the ECM is lost. Search the V6 board with my name as author along with "idle learn." It explains how to do it.

I believe one thread on it also explains the need to clean the IAC and throttle body. This too is important to a good idle.

RBob.

 

RBob, is there any more info on that TSB you mentioned? Is there any specific place where the damage is most common?

As for the original poster, I'd check my MAP signal. Don't know how similar the things are, but my MAF used to do the same thing. Also clean your IAC passage and pintle.

 

the MAP sensor is good. I took out the IAC valve and repossitioned it. the chiltons i have on it says that it should be 1 and an 1/8th inch from the houseing. it was like 2 inches out. still really rough idle, but the car isn't dying on me now(which leads me to believe im in the ball park now). now i did notice a knocking noise and after further investigation, it turned out to be my power steering pump. it was a little lose. I checked it out and it seems that the bearing on it may be bad and its progressivly getting worse. so do you think its possible that the pulley from that may be causeing a greater load for the engine than it can handle under idle? is that even possible? every sensor is good. my coil is good, my distributer is brand new, my plugs are brand new, plug wires are fairly new as of beginnig of summer. I don't believe its a problem with fuel delivery, other wise i believe it would be terrible in acceleration, and it performs great there.(for a v6) Im certain it has spark and fuel. it just seems that it can't get the mixture right while idleing.

 

TSB can be found here:

https://www.thirdgen.org/forums/v6/8...-you-have.html

RBob.

 

Sounds like it's time for either a good IAC cleaning or a new one as the one you have doesn't seem to be working (either clogged or electrically defective). The reason for the pintle extension limit on installation is that the guts of the motor could be bound up if the pintle is extended too far on initial installation (bottoming out and pushing back into the IAC housing). No, I don't think the PS pump is your primary problem, but you'll want to look into a new one.

As for me, I think I'm going to go with the TSB, for one, and replace the ignition module, re-gap my plugs, and replace my TPS (signal is kind of funky with the engine running) to hopefully get rid of my code 45. But that takes care of the problem with the old harness and not the 91 harness...

 

replaced IAC with new one, but it still can't learn idle. I am aware of proper instillation, but it just can't learn idle. I need someone to reprogram my ECM so it will idle correctly. the old IAC is stuck/broken so i just found where it would idle closest to correct and left it. then jimmy rigged my throttle body so it would stay slightley open all the time. it works for now.

 

Check out your TPS. You said before that your engine ran better with it disconnected. I'd check to see if the signal is below .98 VDC between the blue and black wires.

 

TPS has been set to .65 so its good now. it wasn't before, it was at like .32 or something like that, I had a mechanic do that for me, the IAC is not moving at all, so what i did was make a change to the idle screw so the throttle would stay open constantly, and at first it was really working for me I set the IAC as close to a good idle as i could and then changed the screw, so the Idle was a little higer than desired but the car wasn't dieing on me anymore, so it did the trick. well today i went out and started it, it started right up no problem, it was idleing really really good, much lower, i put it in gear and it was great. so somehow the car fixed the problem with a broken IAC valve. It running and Idleing really good right now. so I guess after i changed the throttle's idle level, the ECM compensated, and made the Idle where it was suppose to be. and Im perfectly fine with that. but my fingers are crossed, something new breaks on this car every day. Im sure next week there will be a new problem, but i love the car.


appreciate the replys though