I got this nagging issue with my '08G8GT....My Check Engine light comes on regularly...definitely not the gas cap. I had axel back exaust mod's which really just consist of changing the existing mufflers to Flow Masters. No other mods have been made, yet. She also runs a little rough a idle which leads me to believe a Vac hose connection may have come loose......Any ideas???or has anyone else had tis problem.