well i had the same trouble . found that the turbo was spinning but there were no compressor blades left on it so it was doing nothing , however the umpteen mechanics that had a look at it before i found this changed the hoses to the intercooler , made them more rigid, cleaned out or changed the oil filters fuel filters etc and they all contributed to improving the performance but with no turbo it was a dead duck. Easy to check the turbo unfasten the big black pipe work and get a mirror and look inside the turbo compressor end. look for bent or damaged fins/ blades, Obviously with the engine switched off.. you can feel damage with your fingers easily enough .. if there is any damage get all the pipework cleaned out and flushed out well because small particle of aluminium may be lurking in there as i found out to my cost, as the replacement i fitted only lasted a week because other debris hadnt been cleaned out of the pipes. The turbo spins at 200,000 rpm and it doesnt take much to bend the blades and the efficiency of the turbo falls right off. Several scrap yards will have fairly recent turbos and refurbed ones are available New ones carry a hefty price tag .