For sometime now my 2002 TDI has been going into limp mode when under heavy acceleration in 3rd gear. It revs easily to red line in the lower gears. Usually this does not set a CEL but when it does the code is for intermittent overboost. This weekend since I was doing an oli change I decided to look further into this problem. The car has 310K miles. I recently changed all the vacuum lines. So I put the mitty vac on the acculator and seemed to get good smooth movement with around 17-18 inch producing maximum movement. I then used the Vag-Com VNT to graph N-75 turbo response. The results consistently indicated more boost than was requested when the turbo was in use. The 2 lines pretty much tracked each other separated by about a tick mark. Except under heavy acceleration when the actual boost increased further and then into limp mode. Since the turbo was obviously responding I assumed it was likely the N-75. To be sure I swapped with the EGR N-75, but unfortunately the car can still be made to go into limp mode a little over 3,000 rpm in third under heavy acceleration. At this point I'm thinking it must be the turbo but have a hard time explaining whats really happening. BTW the linkage has never been adjusted so that's not likely the problem. Have i missed anything? If it's the turbo is it likely to fail soon or will it continue on like now?