I just bought a '98 Cobra with apprx. 96k miles. The only mods that I know of are a BBK CAI, a catted Bassani x-pipe and a Bassani catback. Once the car is warmed up and stopped, the idle drops from the normal 800 to about 400-500 for a second then bounces up to 1,000+. It settles back down to 800 only to repeat the process all over again a few seconds later. Also, sometimes when I hit the clutch the rpms drop so low it seems like the car is about to die but it just barely hangs in there. Any advice on what the problem might be?