when you say 'ruff at idle' are you talking about, the car shaking, engine noise, engine missfireing, hesitating to keep running..etc? Hard to give adivce without further detail but general things to check into: -Injector nozzles. When was the last time they were replaced on your car? - Injector return lines. cloth like lines that connect to each injector. Replace every few years. can cause fuel leaks and engine issues(lack of power, rough idling, knocking , pinging etc.) - Fuel Filter getting clogged -Tank alga.