Audi 2.5TDi - Turbo/Vacuum Issues


Registered User
Hi guys,

I have a 2000 B5 thats causing me some headaches.... Basically the turbo is stuck in "low boost" and the actuator will not "dump" allowing it to open the vanes.
Its as if its stuck in vacuum and when i turn the car off and pull the vac line from the actuator it snaps open and i can hear air escaping from the lines in a sort of gargling noise.

So things i've tried, Actuator was switched with another from a spare turbo - no different
N75 valve is brand new genuine pierburg - no difference (just stronger vacuum)
VNT rings/rod have been cleaned and it moves perfectly freely by hand or with a vacuum pump
Vac lines completely replaced barring the one line to the vacuum resivoir in the wing (still to do this)
MAF sensor was replaced last year (genuine bosche)
MAP sensor replaced with a 3bar (Genuine VAG)

The car also has Cummins CR nozzles and a full 2.5" decat, was running perfectly fine until i noticed the vanes were "sticky" or so i thought.
After removing the turbo and stripping it i found the vanes to be moving very freely, i cleaned them anyway but it made no odds.. upon putting everything back to normal i noticed the turbo actuator vac line was in the wrong port so i corrected this on the N75 and now it will not release vacuum...
I have tried it both ways and its exactly the same, no matter what happens as soon as you start the car and the rod moves up it will not allow the vanes to open unless you physically remove the vac line from the actuator in which case it springs back to the "fully open" position straight away.
I have tried cycling the N75 using VDCS (it will cycle perfectly and i can feel the valve coming on and off (faint clack in your hand when you hold it) but no matter what the vacuum will not release and the actuator stays closed unless as i said i remove the vac line from the actuator.

Can anyone shed any light on this?



Registered User
After studying some diagrams.. can someone tell me what the air box vacuum line does? is that to dump the vacuum back to the filter?
If so then i may have answered my own question.