'91 Camaro RS 5.0 TBI/auto. Have had this problem since I bought the car.

Symptoms: Idle drops to around 500 rpm, car starts intermittently running rough, and will stall at stoplights and at low speeds. It feels like a misfire, only lasts a second or two, then back to steady (but low) idle for 5 seconds, then back to intermittent misfire/stalling for a second, and so on and so forth. I can idle it up when I'm stopped by putting one foot on the brake and one on the gas, car still has that intermittent miss at higher rpm's when stopped. The SES light came on for about half a second on the highway one time when the engine was under load before it downshifted, then the light immediately went out. Found code 43 (electronic spark control) stored in history. This was months ago, have not had an SES light or any stored codes since. Not sure if that's related or not.

When it occurs: ONLY after the car has warmed up, ONLY when stopped or below 5 mph, and ONLY when it's below 70 degrees outside. Seems to be at its worst after cruising on the highway, and then getting off and stopping at a light. Car runs like a top until it's warmed up and stopped, and then runs fine again as soon as I'm moving. Never any hesitation or other problems when the car is above 5 mph, regardless of engine temp.

What I've replaced: spark plugs, spark plug wires, cap, rotor, ignition control module, coil, coolant temp sensor, battery, alternator, IAC valve, fuel filter, fuel pump relay, EGR valve, EGR solenoid.

Only other things I can think of at this point are ECM, TPS, MAP sensor, or distributor. Broke the clip off the IAC valve when I replaced it, but had the problem before replacing it. Nonetheless I'm going to replace the IAC pigtail and plug next just in case.

Anyone have any ideas? Can't seem to figure this one out.

 

I'd be searching through all grounds and checking wiring related to the distributor-ecm. Then possibly suspecting the ecm. Rather chase wires than spend money on an ECM after all the other parts that were thrown at it.

 

Having the same problem, figured it had something to do with the EGR valve because I could smell exhaust in the cabin when driving. As you stated, only happens in the cold.

I put a vacuum pump on the EGR diaphragm and found out that the rubber diaphragm is completely torn. I've since unplugged the EGR solenoid so the ECM can't control the EGR anymore.

Just drove it this morning and after warming up the rpm dropped as you described and could barely hold idle. I have to double peddle it home so I don't stall it on the road.

Hopefully replacing the EGR will fix the issue, but I don't like throwing parts at a problem hoping that will fix it.

I also should mention that I got a code 32 after driving on the highway for about half an hour and pulled over to grab the code.

Code 32: MAP (Manifold Air Pressure) sensor
circuit open OR EGR fault OR Barometric pressure circuit shorted.



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Forgot to mention, I also have a 305 ci TBI, mine an '88 IROC.

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lol navy02ws6 bought the whole parts store

 

I replaced my EGR valve first thinking that had to be the problem, and I also got a check engine light for an EGR code on the highway. EGR code has not come back since I replaced the valve though, and that's been almost a year. I also get the MAP code any time I work under the hood and forget to push my rubber vacuum patch line back on the broken hard vacuum line that no one reproduces with the correct fitting to go on the MAP sensor. Goes away immediately after I put it back together though, and stays off until I'm working under the hood and it falls off again.

 

Is there a diagram somewhere that lists all the correct voltages that I should be probing for on the ECM harnesses? Most of them show 13-14 volts while the car is running, but there's quite a few of them that only show 2 volts or so, a few that show 8 volts, etc.

How can I check voltage on the distributor?

 

 

Thanks, Tuned Performance! Looks like I've got my work cut out for me.

 

Didn't have time to run a complete check on every pin yet, but did have one that I thought might be out of spec.

One of my injectors shows 13.7 volts at the ECM, and the other one shows 12.7. This was while the engine was running, and the misfire was occurring. Is one of my injectors bad?

Also tried measuring resistance on both injectors while the engine and key were off, and the engine was cold (no misfire). I got 2.6 for both, which is apparently double what they're supposed to have. Master tech at work measured them with engine and key off, but with car warmed up and exhibiting the problem, got 6.2 on one, and 8.something on the other, which both sound wayyyy too high.

Thoughts?

 

2.5-2.6 is a good reading for the injectors.

 

Could my timing just be off? Didn't see the tech use a timing light when setting it after replacing my intake gasket, he just kinda eyeballed it. That was about 10 months ago.

 

Could be, thevtiming spec is tdc with the est disconnected.

 

Watch your timing mark, if its jumping all over the place then you might have a stretch chain

 

FIXED!!!!!

Timing was wayyyyy out of spec. Set it back to 0, and reset the IAC again. Idles smooth now, and no more stalling!

 

Great news !

 

You're not kidding, I can finally stop driving this car with two feet!

 

To anyone still experiencing this problem after having tried the above suggestions (and checked the timing) I finally was able to fix my rough idle by blocking off the EGR valve (mine was broken), and replacing the cracked vacuum hose going to my MAP Sensor. No more vacuum leak, no more EGR, and finally my car runs properly!