Hi, my 2006 A3 2.0 TDI 140 turbo won't boost - unless I remove the pipe that comes out of the vacuum reservoir - in which case it boosts well. I've spoken to local garages, several Audi technicians and turbo specialists and no one has been able to provide an answer as to why it will only boost when the vacuum reservoir pipe is removed. It will still go into limp mode randomly. MAF, MAP, EGR, ACTUATOR, ETC have all been replaced, and a smoke test showed no vacuum leak. EML has come on several times always showing underboost. If anyone can shed any light on this I'd be very grateful - thank you!