Poor idle when engine is cold

[auxbar]

I have a '94 Grand Prix GTP with the 3.4 engine, 107,000 miles. Whenever I start the car cold, the idle will go to about 2000-2200 RPM, then drop way down below 1000 RPM, then go back up to 2000 RPM, and continue going up and down until the engine is warm. Sometimes, especially if its really cold outside, the engine will stall out when the idle drops down below 1000 RPM. I get a bunch of smoke (kind of white-ish, not really black or anything) while the car is warming up, idle bouncing all over the place. Once the car is warm, the problem gets better.

While driving, the car seems to be OK, no loss of power or anything like that. When I come to a stop sign, the idle will hang at about 1500 RPM for a few seconds, then slowly fall back to 1000 RPM or just barely under 1000 RPM. Sometimes the idle will bounce a little bit between 1000 RPM and about 800 RPM. Engine kind of shudders when this happens, and the exhaust has a "putting" kind of sound. If engine is still cold, has a little bit of hesitation when taking off.

I am not getting any Service Engine Soon light. I changed the idle air control valve, but it did not help. Searched high and low for a vaccuum leak, but can't find one anywhere. I tested the EGR, and it checks out OK. I totally disassembled the EGR and cleaned it up with WD-40. That did not help either. I have a K&N air filter, and I disassembled the cold air intake and totally cleaned it up as well as the throttle body. It really was not that dirty, and that did not help as well.

I took it to a mechanic, and he could not find vaccuum leak. He agreed there was a problem, but he was stumped. He did not think it was the EGR. I suggested to him it could be intake gaskets, but he did not think so. He hooked it up to his diagnostic, but computer did not have any stored codes, which didn't surprise me because I was not getting any SES light. He thought problem could be electrical, or in the programming of the computer. That did not sound right to me, I've had the car for 8 years and never had this problem before.

Does anybody have any suggestions? Some of the posts on here suggest intake gaskets, does anybody have any kind of detailed instructions or photos of how to change these on a 3.4? I'm not to bad with a wrench, but not sure I want to completely tear down the engine to get to these gaskets. Anybody know how to check for intake gasket problem? I took off the plastic 3.4 cover on the top of the engine, which exposed the three front fuel injectors. I started the car, and shot some WD-40 around the gaskets there, but I could not detect any change in the idle. Any help would be greatly appreciated. Thanks!

[richtazz]

when you changed the IAC, did you clean the bore in the throttle body where it goes? it sounds like an IAC sticking, but if that was done, I think your problem is more evil, like an intake or head gasket going, which is common on the 3.4 DOHC.

[auxbar]

Yes, I cleaned out the bore where the IAC valve mounts into.

[ddave]

repl intake gskt, ck fuel pressure regulator

[auxbar]

Does anybody know how to do a test for the intake gasket? Intake gaskets is going to cost big bucks, and one mechanic I took the car to did not think this was the problem. I'd hate to drop big money on the intake gasket without knowing for sure this was the problem. If it was intake gaskets, would I get the Service Engine Soon light? Thanks in advance for anybody who can help.

[theicks]

Auxbar,

I too, unfortunately, had the exact problem with my 1995 GTP and when I brought the car into a mechanic finally, it was the intake manifold itself that was warped. I am wondering if this could possibly be a GM service issue.

[auxbar]

Theicks, did you have your problem fixed? How much did it cost you to replace it? How many miles was on the car when this happened?

[auxbar]

Ok everybody. I had the intake gaskets changed (two lower, and one upper air plenum gasket) and now my Grand Prix is running like a top. These are great motors when they run properly, and GM should have recalled those crappy intake gaskets.