1.9TDI Quattro Boost Cutting out then Limp Mode

[rallyman]

Advice needed please folks.

My A3 1.9 TDi Quattro 130 goes into limp mode when under quite high boost. Prob around 3500 rpm. It does not do the fault all the time. I have had the codes read and it comes up with ' Overboost '. When you turn the ignition off it resets everything and we are at full power again until the next time.

I have had a look around the turbo and it seems ok externally as the wastegate move freely. What I did find strange is that the wastegate moved when I applied vacuum to it and not pressure?? Is this right as a conventional turbo wastegate would be opened with pressure?? Could the wastegate operate externally but be siezed internally??

Any advice would be gratefully appreciated. Thanks

[andrew-spike]

hi, my mate had a problem like yours with his a4,it turned out to be the n75 valve.

[rallyman]

Thanks for that. Does the TDI have a N75 Valve. There are two valves the same located on the bulkhead with vac pipes in and out. Both valves are exactly the same. Are they both N75??