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
