Need help with 97 Cavalier 2.2

[-83MONTESS-]

I have recently encountered a very rough idle when the car has been shut off for over a few hours. The car starts fine but idles very rough and only gets worse when I put it in gear. This started happening a few months ago so I cleaned the IAC and it went away. Fast forward to a few days ago and its back. This time I replaced the IAC all together and it seemed to idle alot better with only a minor miss every once in a while but the next day the horrible cold idle was back and getting worse everyday. The rpms smooth out like normal when I raise the rpm and its fine while driving down the road. Another thing im experiencing occasionally is that when I let off the throttle it takes way longer than it should to idle down. Any ideas here? This is my daily beater and I rely on it. Would a coolant temp sensor, TPS or bad fuel filter create this?

I should also add that the MIL is on but only for an EVAP leak(rusty filler neck) and a lean/rich code that started after the exhaust fell off. I repaired the exhaust pipe itself but the cat has some small holes in it and so does the down tube flex pipe. Thanks

 

[chevy2480]

Maybe a faulty ignition control model behind the coil packs. Seen that a few times on those cars. Also i would do a compression check to make sure your not loosing compression in one of the cylinders. I must have replaced 5 headgaskets on my dad 97 cavalier 2.2 motor. 1st time around 100k then 170k 240k and 300k. Lol
Those motors run forever but are known for headgaskets. Sometimes they leak coolant and other times they blow compression out between block and head and cause rough idle etc.

And yes a coolent temp sensor would cause a issue if reading negative temp butyou can sometimes verify that by unplugging it.

 

[-83MONTESS-]

If it was an ignition module or head gasket wouldnt it do it at different times instead of just cold idle? And for the ECT your saying just unplug it and see if there's a difference?

 

[tetomas]

Have you checked for a vacuum leak? Slow to idle down on a fuel injected engine sounds like a vacuum leak. Check intake gasket and PCV valve.

 

[-83MONTESS-]

Have you checked for a vacuum leak? Slow to idle down on a fuel injected engine sounds like a vacuum leak. Check intake gasket and PCV valve.

I have "listened" for vacuum leaks but not actually tested for any. But again wouldnt a vacuum leak be present more than just cold idle?

 

[chevy2480]

Yes if you unplug the temp sensor it will put car in limp mode and will usually run fine. It could be moisture on module or even a bad wire causeing rough idle once warm moisture is burned off.

 

[Fox80]

I would lean towards head gasket as well, when you shut the car off hot the coolant bleeds into the cylinder and in a way wet fouls the plug leading to a rough idle on start up. Some of the other run issues could be because of coolant burn off, the O2 sensor code you said you have also comes up on occasion, fuel being mixed with coolant leads to a "lean" reading at the sensor. Put a pressure tester on it pump it up to 18psi and let it sit, if it doesn't hold for a while start looking for an external leak, if nothing I would pull the head. Very easy job on that little motor, almost routine maintanence on them like said above. If you have the head surfaced it will go 100,000 mile, if you just swap it probably get 25-45k out of it

 

[-83MONTESS-]

I would lean towards head gasket as well, when you shut the car off hot the coolant bleeds into the cylinder and in a way wet fouls the plug leading to a rough idle on start up. Some of the other run issues could be because of coolant burn off, the O2 sensor code you said you have also comes up on occasion, fuel being mixed with coolant leads to a "lean" reading at the sensor. Put a pressure tester on it pump it up to 18psi and let it sit, if it doesn't hold for a while start looking for an external leak, if nothing I would pull the head. Very easy job on that little motor, almost routine maintanence on them like said above. If you have the head surfaced it will go 100,000 mile, if you just swap it probably get 25-45k out of it

Ok im going to pull a few plugs out today before I leave for work and see if they are wet. Tomarow since im off from work I plan on replacing the fuel filter also. I heard that a bad fuel filter can cause this from not allowing correct fuel pressure on cold start up. Im not sure how much truth there is to that but either way I will replace it.

 

[-83MONTESS-]

So I pulled the plugs today before I started it up and they all looked like this
plug before start by bwollens1983, on Flickr

Then I pulled the ECT connector and the car wouldnt start. Just turned over but never tried to start. I reconnected it and it started up with the same shitty idle. Then I pulled the connector again and this time it kept running and really didnt change much. I let it idle for a few minutes while I sprayed around for vacuum leaks. I didnt find or hear any vacuum leaks but the car stalled out shortly after. I reconnected the connector and it started but now the MIL is flashing and the car sounds the same as it did, no change to the shitty idle. I shut it off, unhooked the battery and puled the plugs again and found this
plug after start by bwollens1983, on Flickr

After I put the plugs back in I started it up again and after a minute or two the MIL started flashing again so I shut it off and called off work :x Im lost from here guys. Wouldnt the plugs be wet or atleast darker if they were getting fouled out or smoke from the exhaust? Wouldnt the car run better after the ECT was unplugged if that was the problem? There is no coolant in the oil.

 

[chevy2480]

Did you do a compression check yet to rule that out?