2.0 TDI BPW Engine Code Overboosting

Hi all! I have a recently purchased 2007 Audi B7 with the BPW (PD) engine that is having the dreaded overboost issue along with a general sluggish behavior. Turbo was replaced 40,000km ago and seems to be working ok. No shaft play and almost no oil in the intercooler. I have pulled a ton of logs and will post them soon. First I just wanted to confirm that the turbo’s actuator arm movement looks correct in this video. Actuator arm was engaged using the VCDS output test. I also detached the actuator and the lever arm could be moved smoothly and evenly. I just wanted to confirm that the vanes seemed to appear free before I started checking other parts. N75 and MAF are next on the list. Thanks!!

https://youtu.be/Ys_3gzv4eK0

I have gone over the logs and couldn’t see a smoking gun reason for the hesitation and overboost. Today I unplugged the MAF and immediately noticed a difference/improvement. Acceleration is much smoother and steadier from a low rpm (though I could feel it wasn’t as quick as it should be). Anyone had any experience cleaning a MAF on a BPW? I am ordering a new one but in the meantime I thought I’d try cleaning the one I have.

I cleaned the MAF with MAF cleaner but it didn’t help. Car runs smoothly with the MAF unplugged but with it plugged in there is hesitation at certain times accelerating. At low throttle I hear what sounds like an rpm dependent chirping/pressure releasing sound which I think is the EGR opening and closing quickly. This only happens with the MAF connected. Could a bad MAF cause the EGR system to go haywire? Would explain a lot of my driving issues if the EGR is opening and closing at the wrong times.

And I’m posting in this forum due to MK5 tdi engines being the most similar to the B7 Audi tdi’s!

I would begin by checking for OBVIOUS vacuum leaks. I have seen vacuum leaks in the hoses around the tandem pump, connecting the booster, the N75 valve and such.

Was it a reputable turbo or a Chinese copy? Chinese TDI parts DO NOT LAST.

Good luck!

Thanks! Turbo was a new oem Garrett. I’ll keep looking for vacuum leaks but as of yet haven’t found any. Would a leak cause these issues even though things seem to improve with the MAF unplugged?

Here are a few logs with the MAF unplugged. One with mbar and one with psi. MAF and EGR default to 550 mg/str and the EGR duty cycle is set to 100.6%. The boost spikes a little.
Drove 160km today and it was smooth accelerating and mileage was slightly improved. Hope to get the MAF on Wednesday.

Actually meant to ask how to post pics now that photobucket sucks?

Replaced the MAF which seemed to help the acceleration from lower rpm’s. But today the overboosting problem worsened suddenly and I could hear a fluttering sound accompanied by hesitation during easy acceleration and then limp mode. I was logging during this time and saw boost spike severely anytime the gas pedal was pressed even slightly. Ran an output test on the N75 and I could see the actuator arm moving fully and seemingly smoothly. Could I have an issue with the N75 not performing correctly or a vac leak in the system? I have checked and will check again. Will try with a new N75 as well. Or could the whole vane assembly in the turbo have come loose/frozen?

Link to a thread I started with pictures attached.

https://www.audi-sport.net/xf/threads/2-0-tdi-bpw-overboost-issue.405510/#post-3508805

Lengthened the actuator rod such that it begins moving around 5Hg-in and stops around 18Hg-in.
Also seemed as though there was/is a slow vacuum leak coming from the vacuum reservoir/vacuum pump vacuum line that leads to the N75. Not bad, just slow and more apparent at lower vacuum. When I increased the vacuum up to 20Hg-in it was almost not apparent. I rechecked all the lines and connections and re-snugged everything and it seemed to help.
As I started driving the car as it was cold (-3C here at the moment) I suddenly had the same fluttering sound, hesitation and the spiky overboost as before as I slowly accelerated. But then I drove very carefully for a few min before accelerating a little harder and things seemed to improve. The log graph started showing almost perfect alignment between requested and actual boost and low-down power was improved with no hesitation.
I think I still have a slight vacuum leak that is more apparent when the car is cold and the engine hasn't built as much vacuum. This seems to be part of the cause of the weird overboosting and fluttering sound. But after driving 20km at all speeds tonight, it now drives better then ever since I bought it.
So to sum up the story: the actuator arm seems to have been too short combined with a slight vacuum leak to the N75 system caused my weird overboosting issues.