2004 Cadillac Deville with random misfire

Question

2004 Cadillac Deville DTS 300hp, changed plugs, proper gap and I got a random misfire

Answer 1

Hi there,

If the engine is running rough at idle you can check for intake manifold vacuum leaks by spraying some carb cleaner along the intake with the engine running. If the idle speed increases or smooths out, then you have a leak. If it doesn't change, then it's possible or even likely one of the coils is the problem. Sometimes it takes the right circumstances for the coils to arc or fail. If it's only misfiring after a long period of sitting the issue could also be with the head gaskets. Pretty common problem on these. A small amount of coolant leaks into the cylinder and causes a miss until the coolant burns out.