I discovered a misfire on #6 cylinder. I went to my friends shop ipmautoservices.com and pick up 5 new coil packs to replace the last 5 stock ones. After completing the install the misfire was still there. So I got a new fuel injector installed but the misfire came back after a few days of driving. I took the spark plug out and used some Mass Air Flow Sensor cleaner to clean off any crap on the spark plug. Installed the spark plug back into the car, took it for a drive but again after 10 mins of driving the misfire was back.
A week later I took the spark plug from cylinder #6 and swapped it with cylinder #5. Cleared the P0306 code and took it for a drive. Few mins later the same code came back up. If the spark plug was bad on cylinder #6 then it should have caused a new misfire code on cylinder #5 after the swap. Have tried swapping the coil packs around and still the misfire is around. So at this point I'm a little lost.
Another week pass and I read on a forum (NWQuattro.com) that some Iridium spark plugs are known for having issues. I figure, I might as well give it a try so I went to NAPA and got a set of 6 OEM NGK PFR6Q spark plugs. Originally following the instruction of several people within online forums I gaped the plugs to .028 inches. I went out for a long drive and all was good for about 60 miles but then the misfire was back... just not as bad. Called my friend up in at ipmautoservices.com and he said to gap them between .016 - .024 inches. I gaped them to .022 and went for a 25 mile drive and all seems good now. I changed my APR ECU program from the 91 oct. to the 93 oct which would increase the timing and that would increase the chance for misfire on a malfunctioning spark plug... in theory. So far there is no misfire but I'm going to give it a good 100 miles before I completely relax. I did check the gap on my still relatively new Denso Iridium Spark Plugs and they ranged from .035 - .045 inches which is way too big... likely that was my problem. It was pretty stupid of me not to check them. I bet if I re-gap them and they will work fine. *Word of advise always check your spark plug gap.