*This is not a thread for posting your own misfire problem!*
Please start your own thread in the General Maintenance & Troubleshooting forum. Feel free to post your own resolution to misfire problems though.
Once or twice a week an individual posts about having a misfire issue. This is a very common problem and there are alot of threads addressing this very problem. So here are the possible issues (read this first,then post about an issue if you have no resolution after trying said solutions):
1. Wrong, worn or incorrect gapped spark plugs. You should run only NGK stock range plugs gapped to .028.
2. Clogged injectors/dirty fuel filter. Try changing the fuel filter. The maintenance schedule is every 30K miles. Have the injectors cleaned or at least run several bottles of a good injector cleaner through the engine. Also make sure you are using the correct octane gas! Either 91 or 93 unless you are specifically tuned for another octane!! (IE: race gas or E85).
3. Check valve clearances & compression. Leakdown/compression test.
4. Oil or dirt build up on MAF sensor. This causes an incorrect load reading which make for AFR corrections out of line. Misfires can result. Remove the sensor, place in plastic bag. Spray out with CRC MAF cleaner or NON chlorinated brake cleaner.
5. Vacuum leaks or preturbo leak. Check where the FPR hose connects (generally you could get a P0457 or P0171 with this as well). Check the turbo inlet pipe where it connects to the turbo. This pipe is famous for ripping and causing a huge preturbo leak (P0171 as well).
6. Clean the battery ground cable and ones that run to the intake manifold. These are sensor grounds and must be kept clean. Clean coil pack grounds (bolt holes).
7. Cam timing. Check cam timing per the service manual. Clean cam sensor face.
8. Excessive PCV blow by. PVC gases will effectively lower the octane content of gasoline/petrol.
9. Carbon build up on motor. Real common on EJ205's. Get some BG Chemtool, GM top end cleaner or other type of carbon remover. GM top end cleaner seems to work really well.
10. Lightweight flywheels or crank pulleys. (phantom misfires) Clean crank sensor face.
11. Bad/loose coil pack or coil pack connector. Test coil pack and move to other cylinder to see if DTC changes. Also check the tower boot for corrosion.
Misfires all cylinders: Coil pack connectors mixed up (black to back),light weight flywheel,bad/unplugged crank or cam sensor,incorrect gapped plugs,cam timing off.