Is it possible for the wastegate to stick open? If i drive at a constant speed were the engine is running at less than 2000rpm and then want to accelerate, the turbo fails to spool up, so I need to drop down a gear or two to increase the revs (some times redlining) before the turbo boosts, however if I keep the engine at higher revs i.e. 2000rpm+ the turbo boost is always there. Had a new MAF fitted, but hasn't helped; only when the turbo boosts the acceleration is stronger than before.

cars are too expensive....try a broom like mine ....cold but fast. xx