I have the same problem!. I have a 2005 1.9Tdi with 100k. Car can shake/judder on starting and again judders when changing up thru gears, along with apparent loss of power. I have corrected by switching off and on again (works sometimes) but it does come back again. I had it in a car electrics garage for a parking sensor and they said there was no other faults showing. I have been told it may be the dual mass clutch - could it be? or any other thoughts?