I have a 2000 jetta 2.0L and have had this problem for about 6 months. Sometimes when i'm at a red light, my car starts accelerating for nothing, can go up to 2000rpm and if i put it in neutral, i goes up to 3000rpm. I have to press the brakes real hard for the car not to move. Usually it doesnt last more than 15 seconds and happens about once a week. Also in winter if temperature goes under 0 (32F) my car has a lot of trouble starting, like if gas doesnt get to the engine. This also happens pretty easily if my car is parked on a hill where the front end is higher. I'm suspecting the mass air flow for the idel problem but i'm a newb in VW mecanics so if anybody has suggestion it would help.

Also the check engine is always on and has been evern since this problem started. Even if i reset the computer as soon as i turn the key and start the car it comes back on.

 

I brought my car to the dealer, officiel VW dealer and my problem was the water temperature sensor. For some reason, the name of the sensor is not really what it is, in any case it gave false readings to the computer and screwed up my idle and other stuff. problem solved