I've got a 98 M6 Z with a fully built motor, ported heads ls6 intake ls6 cam MAC headers etc. Here's the problem; the check engine light has started to come on and off periodically and it sounds like there might be a serious exhaust leak somewhere, but I know that can't be with the check engine light right? My buddy has had a similar problem and said it popably is a bad valve: floated or chipped. The idle is kind of shaky as well and it stutters coming out of 1st and 2cd. PLEASE HELP, comments usggestions diagnosis
ps- took it up to autozone to get code scan and it didn't come back with anyting because the check engine light wasn't on

 

Kind of sounds like a missfire, usually when you have a cylinder misfire the check engine light either will blink or turn on and off. Scan it usually the ecm stores the codes for a certain period of time, Autozone scanes ecms for free if you don't have an access to a scanner.

 

scanned it at autozone and nothing came up, the code only seems to come on when I'm driving the car

 

I don't know if AutoZone's scanners read the scan history/memory. At least they didn't pull mine from history and the guy told me the light needed to be on to pull the code. I bought a DigiMoto ($100) and it pulls all codes

 

well, took the car to the dealership today, and to my surprise it wasn't a misfire, spark plug, valve or pushrod. It was one of the rockers on the drivers side. It had worked its way almost completely loose, and $152 later the car is running fine.

NOTE to all: If you change camshafts more than twice, make sure the rockers are tightened down good, otherwise you can run into some serious problems