Success at last.... our C 250 CGI is quicker than the C200 CGI !!! There is a Turbo Boost valve on the Turbo Housing which retains some Boost during up shifts (Now I know !) Made of Plastic with Neoprene O Rings and an internal spring which after 10 years gets tired. Coupled with a Turbo Boost control Valve (Two different animals) a better driving Car. The Boost Control Valve alters the opening of the Waste Gate.... an after market fitting to increase Boost across the range...