Most likely the Turbo is not boosting enough (not supplying enough air).
There are several reasons this could be happening, and it is too complicated to explain over the internet.
Here is a video about inconsistent boost on a BEW TDI:
If boost is OK, then you might have an EGR problem.
If the EGR is OK, then you might have Camshaft lobe issues.
You might want to find a VW Specialty Garage to diagnose this for you.
Unless an Expert from this site is willing to help.
Friday, August 23rd, 2013 AT 3:26 PM