One of the hardest codes to track down.
The system has detected a misfire that cannot be attributed to any one cylinder.
The best way to go is cheapest first, so install new, properly gapped spark plugs and replace the plug wires. That will leave only the much more expensive coils and ignition control module for that system.
If no change then move on to the fuel system before spending big bucks.
also this could be caused by bad fuel performance or clogged injectors so change the fuel filter, check fuel pump performance, and first try a fuel injector cleaner before removing and cleaning them or replacing them.
O2 sensors are relatively cheap and could possibly set off the code.
If all this fails ( basicly what you have done is a tune up) I suggest having the car put on an engine diagnostic computer to possibly track down the source of the misfire.
Changing out any of the more expensive parts without knowing if it will repair the problem is not a good idea and is costly, an engine diagnostic will cost around $100 and is well worth the money when the tune up has not improved the situation.
Trouble code P0300 means: Random/multiple cylinder misfire detected
P0300 = random misfire. Could be as simple as needing a tune up.
What is happening there is that the computer may not be able to detect the misfire in the electrical system, but is finding too much raw fuel downstream in the catalytic converters that tells it that the fuel is not burning completely, thus a misfire. Could indicate that the problem is mechanical not electrical.
p0303 is cylinder #3 misfire
2006 Pontiac grand prix recurring number 4 cylinder misfire diagnostic code? What could it be?
Cylinder number four misfire.
Cylinder #1 misfire.
misfire cylinder #5
Cylinder 1 Misfire Detected
Most commonly a bad plug or wire. If not that, then coil.
replace the coil bar and you are set
P0305 is cylinder number five misfire detected.