Hello,
I have a 2005 Chevy Cobalt with a 2.2 engine that is idleing rough when in idle and when accelerating. I took it to a local dealership and they reported that cylinder #4 was misfiring and that I needed to replace the Ignition Control Module. They were going to charge $300 to do so. I said NO and bought one at AZ for $90 and replaced it myself. Unfortunatly it didnt fix the problem.
I took my car back to AZ and had them scan it. They got a P0304 error. Which is a misfire in cylinder #4. They suggested new spark plugs since i have 93K miles on the originals. So I bought 4 new Autolites and replaced them. Also since i had it apart I rotated around the boots because if it continued to misfire and the misfire was in a different cylinder then I knew it was a bad boot. Well needless to say neither fixed the issue and its still misfiring!
I took it back to AZ and they scanned it again and it got the same P0304 error with a misfire in cylinder #4. I am not sure what to try next. I cant keep dumping $$ into the car. Any suggestions? I am thinking the Ignition Coil pack needs replaced but I am really grabbing at straws.
Not sure if this would have anythign to do with it but when it initally started acting up I was pretty low on gas, like almost to the red line. Since then obviously I have put gas in it.

 

Welcome to the forum. A lot of people, including those who should know better, misinterpret "misfire" codes. P0304 just means cylinder #4 did not contribute sufficiently to the crankshaft output. Anything to do with the spark is one possibility but so is an incorrect air/fuel mixture or a cylinder compression problem. It sounds like you need to find a better diagnostician than some guy behind a counter at AutoZone.

 

See thats the thing I took it to a local Chevy Dealership to begin with and they said it was the Ignition Control Module, mainly based off of the code that it was reporting. I honestly cant afford to take it back to a dealership to have them look at it again.

Is there any way I can test the air/fuel mixture level? What do I do to test the cylinder compression?

 

I'm really having a hard time with how the ICM diagnosis was arrived at "mainly based off of the code" but I'll take your word for it. The tests you're asking about, you'll probably want to take it in for service. Try an independent repair shop.

 

Well thats all they told me. "We scanned the computer....got this code...says you need a new Iginition Control Module. That will be $300 for parts and labor."