Oliver,
It depends on what the problem actually is, it could be as simple as a dirty throttle body causing a mass air flow sensor fault and all you would need to do is clean the throttle body with carb cleaner. It could be a mass air flow sensor problem and cost $400, it could also be a faulty throttle body which would cost a thousand or more. To know for sure you really need to have the vehicle scanned. Do you have a check engine light on too?
Danny
VW Mechanic
ASE Master Certified with L1 Certification, Volkswagen Certified, VW and Audi repair shop owner