Boost leak test your car. Sounds like you have a leak and it's causing you to run so rich under boost that your car shutters.
Your turbo pulls in air (which is metered before the turbo). Fuel is being supplied for the air that is supposed to be going into the engine - instead the air leaks into the atmosphere, causing a rich condition. If you push it hard enough you will hit fuel cut.
Last edited by Skip; Sep 1, 2008 at 01:19 AM.