a new (n75) wastegate control valve may fix this. failing that the turbo flow control vains are known to stick on the diesel engines so a three part cleaner may do the trick its called innotec turbo cleaner.
http://www.turboclean.org/ try this site to order it. if memory serves me right its about £30.
if both of these dont work then its time for a new cleaner. i have no doubt if you were to scan for fault codes it would come up with overboost limit exeeded.
jamie16v
January 2011
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