I have a 94z28 with 115000 mi on it. I have this rough idle problem as well as a running rich issue.

The idle feels like the car has a rough idle cam in it. I was not the original owner so I don't know that. When I am at a stop light and take my foot off the brake the car kind of chugs before i accelerate. While my foot is on the brake she shakes, noticeably. The exhaust is very rich and I don't know if the problems are related. Here is what I have done to the car lately:

New o2 sensors (Bosch)
New plugs (Bosch 4) and wires
New distributor
New EGR
Cleaned throtle body
Cleaned IAC
Cleaned MAP and replaced boot seal
Installed 1le intake elbow
New TPS
New Tranny
New starter
New belt and tensioner
New PCV

When I bought the car it had the rough idle problem and after all the above the problem still exists. Car runs great at cruising speed and on acceleration. I have a Flowmaster exhaust with a single cat. I have checked all the vac lines that I couldn't find and everything seems to be tight.

If anyone could give me some suggestions I would appreciate it. I was thinking of taking it to the dealer to check the PCM. Maybe it needs to be adjusted. Richness could be from the fuel air mix being off, but could that cause my idle problem? Would PCM reprogram help? What do you think?

 

I was thinking along the lines of a PCM problem. Maybe you could try to reset it by pulling the fuse labeled PCM Batt in the fuse box. Are you getting good gas mileage? Another thing is... does it do it if you put it in neutral? How about with the A/C on or off?

 

It does idle rough in neutral as well. The AC makes it a little worse. Gas mileage is fairly poor. Is the PCM fuse in the fuse box under the drivers side hood, because I did not see a fuse for it in there?

 

I didn't notice whether you checked or replaced the fuel pressure regulator. After you shut it off, pull the vacuum line off the FPR and see if it's wet. If it is, that means the diaphragm has a hole in it and it is feeding fuel back into the intake and causing bad fuel mileage and poor idle.

 

I will try that, thank you. I pulled it off yesterday but it was in the morning after it sat overnight and probably didn't give me a true idea. I'll let it run a bit first.

 

I would say get it tuned dude.

 

What does that mean DUDE. He's replaced everything that could be replaced. DUDE. Any more useful suggestions DUDE.

 

Today I was poking around under the hood and noticed that the gasket under the top cover to the throttle body was not intact all the way around. I removed the top cover (rectangular shaped piece) and the gasket was totaly deteriorated. I am thinking this is my problem, what do you think?? The gasket was also very wet with oily fuel smelling residue. Anyon know a part number for that gasket? I need to go to the dealer and get one.

 

it will be oily but it should not be deteriorated. You can either put gasket sealer around the edge and put it back together or buy a rebuild kit....

TB Gasket kit - 17113074

Good Luck, and thats probably your problem

 

Thank you, I will let you know my results.

 

I wonder if a damaged and leaking TB cover gasket would cause the richness problem.

 

Definitely....Any unmetered air after the MAF will give a false reading.

 

I replaced the damaged TB cover gasket yesterday and the car runs a little better, however it still has the same syptoms as before. I used a stethescope and listend to all the cylinders and injectors. Everything seems to be normal. Almost as if it's not getting enough air. I was thinking of getting a cold air intake a while ago. I wonder if that would help any?? Any more suggestions?

 

this may not apply to you but just in case.


I see that you replaced your Bellows... One time I removed mine and when I put it back I didnt do it right... the bottom portion of the bellows that conect to the TB got caugh on somenthing and did not slide over the Throttles. I ended up with a huge intake leak and my car gave me *****. now in my case It felt it was running lean though... would you check your Bellows to make sure they are installed properly?? mine look just fine from the top.. it wasnt till I removed it again that I noticed it was pinched and was not all the way in.

Marvin

 

Oh I just remembered... somewhere in these posts I read one of a guy who had a rough idle and running rich...

He had a leaky injector. Once replaced his car ran fine.


do a search maybe youll find it

Marvin