Injection timing retarded (i.e., fuel being injected late)? The injection timing should be kept up close to the advanced edge of the spec but still within spec.
The timing will retard slightly as the timing belt stretches a little bit over its life. When was the timing belt last changed and who did the work? How was the injection timing verified after the timing belt change? If the "mark and pray" method was used during a timing belt change, it's totally wrong and needs to be fixed because valve timing and injection timing are both retarded.
If that's the case, get the car to one of the TDIclub gurus like
oilhammer to straighten it out.
Good luck and
Welcome to TDIclub.