browning11

In the past few weeks I've been experiencing issues with my 2007 Cobalt LT. The check engine comes on and goes off intermittently. But every time it's the same code P0304, a misfire in the 4th cylinder.
The car has less than 64,000 miles on it and I really only drive it to and from work and around town which is less than 15 miles a day. I changed the spark plugs, and the light went off for a day or two but then it came back on. I changed the coil pack on the 4th cylinder and that seemed to work a little while longer but ultimately the code came back. I took the car to a garage and let them do a vacuum leak check and it came back negative for leaks. My only other options are either the ICM or a defective computer. I guess it could be the catalytic converter but the exhaust doesn't give that rotten egg smell.
The car has a rough idle at times, some times it's worse than other and then when I begin to accelerate like at red lights or stop signs the car jerks. I'm not really sure what else to do, any suggestions out there. Also does anyone know where the ICM is? I've been looking but I'm unsure of where it's located. If you know where it is, I'd really appreciate a picture or some detailed directions.

browning11

I forgot to add that I've changed the gas cap because the old one was a loose fitting and I seafoamed the motor, via the vacuum hose. I really have no idea what to do next. I have to get my car inspected soon so I can get a new tag and it wont pass with the light on. I can turn the light off but that obviously isn't solving the issues.

I need help. Any ideas crazy or not, I'm kind of desperate.

05g5

yea, compression and leakdown test. Its worst case senario, but good to rule that IN or OUT as soon as possible and your not throwing money into a bottomless pit.

browning11

I had the compression checked earlier today. It's at 85 in the 4th cylinder the others are fine. The mechanic gave me a $800 quote to fix it. However when i asked what was wrong with the car he just kept repeating the quoted price.

Tomtwtwtw

He kept quoting it likely because he doesn't know exactly what is wrong. There are a few things that might cause low compression, and hard to really pin it down until you get in there and see what it is. Maybe bad piston ring, maybe valve issues...unfortunately the cost is always big since a mechanic has to get in there and start tearing apart the engine to get an accurate diagnosis.

05g5

Ok, so you know its no longer, plugs or coil related. or a simple fix.. seafoam wont help

Stop throwing money at it, and have it professionally looked ( or do it your self if you can wrench ), pull the head and have that checked. I would natrually HOPE this is you issue, and not a blown ring / mashed sleeve, that will get costly. Doing a valve job, costly yes but not as bad.. but no motor pulling and costly machine shop bills. to re-sleeve, do piston/rods all that other stuff.

machine shops, i will say generally will cost you $200 to check, mag, clean, resurface your head. But at that point you will KNOW you have a bad valve, or bad vale seal so to speak. cuz they will tell you it failed.