throttle surge

At a full stop, the engine throttled up severly. The problem has reoccured a few times over the last two days. When the brake is taken off the car lunged away and accelerated to appx 30mph, then chugged. Diagnostic suggestions?

Originally Posted by OX

At a full stop, the engine throttled up severly. The problem has reoccured a few times over the last two days. When the brake is taken off the car lunged away and accelerated to appx 30mph, then chugged. Diagnostic suggestions?

IAC valve malfunction? Taking it off the car and cleaning it with carb cleaner might help. It's controlled by the a Idle Speed Control unit and the Motronic (depending on year). There a good explanation of testing procedures in the Bentley manual. Otherwise maybe it's a vacuum leak? I'd clean the throttle body and Air Flow Sensor too.