Hi all I drive an audi a6 1.9tdi se avant 130bhp. When the turbo kicks in the brakes are good too. The brake pedal only needs a light touch at the top of the stroke to brake, pointing to a problem in the vacuum system but i 've had all vacuum system checked out by 2 audi garages.No fault found. Is there a check valve in the pipe to the servo? and could this be the fault? Cheers and Merry Christmas to all.