2008 Pontiac Grand Prix 3.8L My car has a P0300 diagnostic code. Check engine light is on, and typically flashes if I exceed about 30 miles an hour. How can I fix this?!

Stephen Denton

Asked by Nov 30, 2015 at 09:00 AM about the 2008 Pontiac Grand Prix Base

Question type: Maintenance & Repair

I have changed my ignition coils,
cleaned my throttle body, egr valve,
and added a bottle of fuel injector
cleaner into my last tank of gas.
Worked fine for about a week and
started again. It has an occasional
low rough idle, and loss of power.
And has bucked on me a couple of
times. I am thinking it may be a
timing belt issue or a camshaft
position sensor. I am just trying to
figure out my next step. Please

2 Answers


Sounds more like a clogged catalytic converter


po300 is a random miss fire. First thing that comes to mind is condensation in the gas. Try that red bottle of Heat, something with isophrofel in it to break down any water in the gas. Otherwise with this code would be plugs and wires, but you said it ran fine after the fuel injection cleaner.

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