could somebody please tell me the normal rpms while sitting at a red light. i noticed my car goes from like around 800 and then sometimes drops down to like 500. i just recently replaced a couple coils and all my plugs but the misfires still occur. is that just a normal side effect. and also my car only seems to mis while at idle, not while driving at all. does that still sound like a coil issue? any imput is appreciated