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Rev and stumble at idle

Fuel System

Model: Carrera, Year:2004, Mileage:95,000, Type of use:Street use only
I have a 2004 996 with 95,000 miles. This car is a champ. It's running very well except it has an issue at idle. When the car is at running temperature, I will be stopped at a light in gear (Tiptronic) and it will throw a small rev, 200 to 400 RPM, like if I had tapped the gas pedal, or it will stumble once, and then it will be fine. There is no warning or symptom before this happens and it happens randomly, perhaps once or twice a day. There is no other issue, the motor runs fine around town and pulls without hesitation under heavy acceleration. It did just fine on a long freeway drive out of town. My dealer cleaned the throttle body (sp) on the first visit and the issue continued and they were able to duplicate the issue on the second visit so they know what I am talking about. They did a smoke test and found two air vacuum leaks and made repairs. No other leaks were detected and there are no codes showing any problems. After the leaks were repaired, the issue is continuing. They are hesitating to replace the MASS air sensor/controller because of the expense and they are not yet convinced that this is the problem. Most of the time, the rev issue will happen if I am sitting at a long light. But I will get stuck at a series of lights and nothing will happen. Then at other times it happens almost immediately upon stopping and always at idle. Though the revs aren't enough to move the car, I am keeping my distance from the cars ahead of me and from my garage wall, foot firm on the brake pedal and hand ready to take the car out of gear, just in case it becomes more that a quick rev.Many thanks,Mark

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