95 2.3L Rough Idle

Hello all,

New to the forum, but not to cars. :biggrin: I just bought a 95 Grand Am with 2.3L and it has a problem with a miss at idle and through out the RPM range. But on initial startup, it runs fine. I start it and it runs smooth for 2-3 seconds and then starts to miss. I'm guessing that it has to do with the fact that it runs on a predetermined set of parameters for so long and the the ignition module takes over. I'm thinking that the problem is either the ignition coil housing and / or the ignition control module.

The number 1 plug is being fouled out, but 2, 3 & 4 are fine. Compression is good and even across all 4 cylinders. Ign coil resistance is ~6 M Ohms, which according to the Chiltons manual is low and they should be replaced.

I understand that the ignition coil housing is notorious for problems, but I am unsure of what to look for other than cracks and carbon tracks. There is a ground wire that sticks out from underneath the housing, which doesnt look right.

Thanks for a great forum, I've read through quite a bit and fixed a few problems thanks to the messages here.

Louie

Ok, I've bought a new coil housing and will see if this cures the problem. But does anyone have any other ideas?

Also, can someone tell me what I should be looking for with the ignition module? Is it possible to have this type tested at the local Auto Zone?

Yes Autozone should be able to test it. Usually when they go bad the car won't run. The new coil housing should make a world of difference though. The only other thing you may want to check is the crank position sensor. They can go bad and cause misfires too. If memory serves it should be located just above the oil filter on the 2.3.

Thanks for the info. I'll definitely check the CPS this weekend.

Ok, I replaced the ignition coil housing and crank sensor. Runs much better! ... but I still have the misfire issue.

My new direction has to do with the exhaust. During the misfire, it is sucking air back in through the exhaust pipe. :eek7: I remember reading something about this somewhere, but cant find anything on the site. Can someone tell me exactly what this means??? Please? Thanks! :biggrin:

You could have a burnt exhaust valve that is causing the problem. Have you done a compression check on the engine lately? This would account for the drawback through the exhaust and could be the souce of the misfire.

I have done a compression test ... the readings were good on all four cylinders, but the #1 cylinder seemed to vary quite a bit - not consistent. It looks like you may be right.

Can you explain how this happens? I dont quite understand how a burnt exhaust valve can suck air back in...

When the piston draws down on the intake stroke it will pull gases back through the exhaust valve thus causing it to suck air back in. This problem was far more common on engines before unleaded fuel but it still can happen. The only way to tell for sure if the valve is burnt it to remove the head and examine it. You will be able to tell immediately once you look at it that it is burnt.