loss of power?

Air Mass Flow sensor is the "normal" culprit for this issue (going by your description).

Also the EGR valve along with the swirl flaps in the inlet manifold can be all coked up.

You could try a bottle of Cataclean (Halfords sell it now) as that's fantastic for cleaning up the internals of the engine.

Did you get this sorted in the end and where are you in the UK ?

Paul
March 2014

check intercooler/inlet hoses for splits,remove turbo inlet and feel for play in the impeller

cdc
February 2014