2008 Grand Prix base model random misfire multiple cylinders. (P300)
25

Asked by DannyIcefire Aug 06, 2018 at 08:15 PM about the 2008 Pontiac Grand Prix Base

Question type: Maintenance & Repair

Hello,
I have a 2008 Grand Prix base model with 170,000+ miles on it. I have been
experiencing random misfire on multiple cylinders for a bit. It idles rough, rpm
at start is between 500 & 1250. I have a basic code reader and have mainly
seen the multiple cylinders code come up, but I have seen a single cylinder
throw the code during idle, cylinder 4. I have replaced the spark plugs, wires,
coil packs, and bank 1 senor 1 o2 sensor. This is a sometimes issue because
the engine will hit on all 6 and run fine for a month or so, then back to random  
misfires. I think it might be a fuel issue because it seems to misfire less with
higher grades of gasoline. I’m looking for either a quick fix, or a detailed list of
things that can checked with relative ease since I don’t have handy access to
a garage.
Thank you,
DannyIcefire

2 Answers
7,465

Brianator answered 6 years ago

Could be a vacuum leak, a leaky fuel injector, a burnt or leaking exhaust valve or alot of carbon buildup in the cylinders. Does the car burn much oil?

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25

DannyIcefire answered 6 years ago

Not that I have seen. I can go the full time the computer determines between oil changes with adding only a quart of oil, if any. I could use a reference for vacuum lines, but I’m pretty sure I’m not hearing a leak. I’ve not smelt exhaust, but I don’t know how to check for a burnt exhaust valve. The only other things I can add are that I’ve cleaned the MAF sensor(reduced engine power problem), it still misfires, and I do occasionally smell gas as I shift into reverse after the car has been sitting for 10 or so hours.

Mark helpful

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