2009 Chevy Malibu Misfire Code 3904

cheapster8

I have a 2009 Chevy Malibu that is giving an 3904 misfire code, which appears to be a misfire on cylinder 4. The malibu has about 105k miles. I have replaced the spark plugs, and the ignition module and fuel injector for cylinder 4 with no luck. The misfire code appears to come on when the car is warmed up and has been idling for several minutes. The engine runs smooth at high speed, and appears to run smooth for a while at idle after I clear the error code. The error code comes back when I pull up to a stoplight or am in heavy traffic (idling). The only misfire code I have seen is 3904.

Dumb question... 3904 error code is for cylinder 4, right? Not the 4th cylinder in the firing order?

Any suggestions on what to try next would be much appreciated. I'm just about ready to take it to a mechanic or even the dealer.

Thanks.

cheapster8

Some additional information. This is the 2.4L 4-cylinder engine. When this error code first started showing up, I could clear it and the car would go a few weeks before the misfire code came back. This was about a year ago. Last week the car was idling very rough. I cleared the code, and restarted the next morning, and the car was idling fine. The misfire code came back the next day, but the car has not had the noticeably rough idle since.

cheapster8

My mechanic did a compression test on cylinder 4 and it was not holding pressure. Cylindar 4 had two burnt exhaust valves. This car only has 106k miles, has never been driven hard or abused, and never gone more than 4000 miles without an oil change. Probably the last Chevy I'll ever own.