Thread: 2008 Grand Prix Base Possible injector issue Code P0305

2008 Grand Prix, Base 135,000 miles, auto trans. I replaced spark plugs about 6 months ago. Engine ran just fine. No codes. I recently decided to clean electronic Throttle Body as I noticed it was quite dirty/gummy black stuff. Removed Throttle body and cleaned with throttle body cleaner. At that time I noticed additional dirty/gummy black stuff in the plenum, which I also cleaned inside as much as possible. Also removed EGR and sprayed with TB Cleaner as well. While I was at it, I used Mass Air Flow Sensor Cleaner for the MAF. Now the engine runs a little bit rough and engine light blinks when I accelerate. Additionally, car now throws Code P0305. Is it possible that I might have clogged a fuel injector during the cleaning of the Plenum? If so, is there a DIY method to clean the injectors? Any ideas are appreciated. Thank you

Originally Posted by Fivefingerdeathpunch

I find it easier to just go back over what you have done.

Cylinder 5 is on the front, closest to the air box. I would just pull the plug wire and spark plug and inspect them. Then swap the plug with cylinder 3 and see if the misfire moves. If not, swap the plug wire, then swap the coil packs around and see what it does. Once you know it's not a spark issue, then look into swapping the injectors around.

I'm not sure I understand what Cylinder 5 spark plug has to do with this problem. I haven't touched spark plugs in 6 months. The problem started yesterday after cleaning Throttle Body, EGR and Plenum. Can you explain further? Thanks.

[QUOTE=Fivefingerdeathpunch;1424993]P0305 is a cylinder 5 misfire code.

Misfires are either ignition related or fuel related. So something is wrong on the spark plug/plug wire/coil pack or it's an injector problem.

Just because you've done the plugs a 6 months ago, doesn't mean they aren't the problem. Start with one thing and work to the next to solve the problem.[/

OK, Engine Light is off.
I re-cleaned EGR and removed Heat Shield from #5 plug. Car ran great. Of course I couldn't know which procedure fixed the problem. Sometimes it's hard at my age to remember, when you're up to your arse in alligators, it's difficult to remember that your job was to clean the swamp. At any rate, I then reinstalled the Heat Shield for plug 5 and sure enough the performance decreased and Code P0305 reappeared. Erased code P0305, removed said shield, no more code or performance issues. Anyway I want to thank Fivefingerdeathpunch for his/her invaluable assistance and others who took their time to read my issue.