As said above possibly the vanes are sticking in the VNT turbo. There’re plenty of videos on YouTube explaining how they work and
how to clean them.
I started having problems with my TDI 110, driving it hard made the
problem go away for a while. Then started doing a lot of motorway driving 3 years ago and not had the
problem since.
Personally I’d recommend:
Scan for fault codes
Check the VNT actuator rod moves freely – if not clean the turbo as described above.
If the rod moves freely, check/replace the vacuum line to the actuator.
If you still have a
problem check/replace the vacuum control valve on the firewall behind the engine.
I fixed my TDI 110 by driving it regularly for over 30 minutes to get the turbo hot.