Are you getting any engine management/flashing glow plug lights?

I've just had to replace the EGR valve at 90k, car was smoking and loss of power, with flashing glow plug light. New valve and its fine..
Also, the hose from the intercooler to EGR valves are prone to splitting, but the split only opens up when the turbo is boosting... But you did say you checked that...!?!
If none of those are your problem, you may have a poorly turbo...