I just bought a used 2001 seville STS, It is in remarkably clean condition. After driving it home and around a little while I figured out why. It started flashing SES light, I pulled a code of P0300, random misfire. After driving the car and then coming home at idle it is running rough. I changed the plugs and wires. it idled clean and smooth, so I drove it around town, and after stopping it started idling rough again. Same code, at idle the code is current however if I idle it at 1500 RPM, and scan the codes again it shows up just as a history code not as current, only at idle does it misfire. The next step would be the coils, and at $250 bucks I'm a little hesitant, without some confirmation. The next step after that will be to the dealership, for a check up.

 

did you have the battery checked?

see this clip :

How To Fix P0300 random misfire codes in your car - YouTube




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I will try that tomorrow, keeping my fingers crossed.