I am sorry if this thread is in the wrong spot. I was looking for another one regarding misfires but I did not see one.
I have a 2004 Grand Prix N/A 3800 with 140,100 miles on it. It is giving the P0302 Cylinder 2 Misfire code while at idle. It does have a rough idle and shifts into reverse and drive with sort of a clunk too (more so into drive than reverse). You can feel the misfire at idle and you can see it on the tach. Other than at idle, the car runs, drives, and shifts perfectly fine. The CEL light will start off by flashing and if you take off driving, such as from a stop sign/light, the CEL will go off. If you leave the car sit there and warm up, the CEL will go to a steady light and I have to clear it with my scan tool. (I do have an Actron CP9185 and a Scanguage II if anyone needs me to run some tests for a particular reading for troubleshooting this issue).
Before we go through exchanging a bunch of messages about what has or has not been checked, I'll provide a listing below of what I have either verified, or have replaced.
Spark Plugs - New AC Delco Double Platinum - Gap 0.60 (CHANGED TO AC DELCO IRIDIUMS)
Spark Plug Wires - New
EGR Valve - New
MAP Sensor - New
PCV Valve - New
MAF Sensor - New
Camshaft Position Sensor - New
Crankshaft Position Sensor - New
Ignition Coils - All 3 - New
ICM - Used. Tested as good.
Fuel Injection Pressure (at fuel rail) - Tested good @ 56
Fuel Injectors - Noid Light Tested. Number 2 is new. I even went one by one and unplugged them and verified that the idle changed when unplugged and idle restored after plugging them back in. I moved the original #2 injector to #4 and the issue stays on #2, even with a new injector.
Compression Test - May need to be redone but the last time I checked it a couple of months ago it was at 137 on the #2 cylinder. Without having my notes in front of me, the best I can remember, all of them were above 130.
Air Filter - New
Head Gaskets - 6 months old
Upper and Lower Intake Gaskets - 6 months old - No leaks that I have been able to locate. No leaking antifreeze through tailpipes or on the ground, no oil in water or visa versa. Everything checks out fine in that aspect.
Coolant Temp Sensor (and plug) - New
Thermostat - New
Throttle Body - Cleaned
Are there some vacuum lines somewhere that I have not located that could be causing this?
