Check eng light

I have a 96 lumina with the 3.1 motor. I have had the check engine light come on several times. When I pull the code it gives me PO300...random misfire. Seems like isolated problem..misfires, sets the light and then runs smooth. Have changed fuel filter and a bad vacuum line. The light doesn't come on until the car has been driven about 40 minutes or so. I am at a lost as to what else could be causing this...any suggestions would be GREATLY appreciated. Thanks Dave :confused:

random misfire? Could be the ignition module, coil packs, or even bad plugs and wires. If its random, I'm leaning more towards a spark problem versus a fuel problem. I think its early stages of a failing ignition module.

New plugs and wires, if you got over 70K would be a good start. Make sure your wires are routed where they can't lay down on something hot or grounded when they warm up and relax.

So are you saying that the ECM seems to be compensating, and correcting the problem as soon as it registers misfire?

Plugs, wires, coil packs and lifters, manifold gaskets were all replaced 5k miles ago. Don't know if ECM is correcting or what. After checking and resetting the light car drives fine for 40 minutes or so, then misfire, light and then runs good...as matter of fact motor is as quiet and runs as good as the day I bought it. Good pick and smooth acceleration, just this pesky misfire.

This happened to my 96 lumina, took it to repair shop and the oiled up the spark plugs and wires, closed the hodo and tunred the lights off. You could see electrical archs between the wires, which caused the random misfire. I would check into your spark plug wires.

So you actually feel the misfire, it's not false registering? They usually have to occur like 20X in a row from one cylinder for the ECM to ID the bad cylinder. Might want to reach back there and make sure there doesn't seem to be a cracked insulator on one of the back plugs. It's easy to do, when replacing them.