so... took the car in to a specialist turbo shop today to diagnose and check. all fine... vanes are not sticky at all, arm moves freely without catching. No boost leaks, No leaks in the vacuum lines at all.

the problem is something he has never come across before... on the old mk4 tdi you had a n75 valve which sometimes gave hassles. mk5 replaced with a vacuum solenoid box (Part no. 6q0906625e). Normally these don't give hassles.

Starting the car up- the vacuum solenoid box controls and moves the turbo arm from rest and into low boost area. But... when switching the car off, the turbo arm "shudders"- almost hesitantly back to the rest position.

it is at this exact same time that the vacuum solenoid box makes the noise which i posted about in another thread ( http://vwclub.co.za/forum/viewtopic.php?f=91&t=167643 ). Basically- the pressure is not held and distributed properly by the vacuum box.

This same "rest" position is also high boost when driving under load conditions. The vacuum solenoid box is not releasing the pressure on the turbo cleanly and evenly, which explains the p0234 error (over-boost) even though the vanes are not sticking.

Such an interesting find for any that experience P0234 on a vw. It may not be the turbo sticking...

This is the most logical explanation after all the testing and also using VCDS.

I got the overboost (p0234) error once when I did 2xxkm/h+ on my polo.
Car went into limp mode, reset the limp mode and the next day the one injector failed.
Don't know if that was the cause of the overboost

Fitted second hand vac box with same part number now- problem solved. car is more responsive and no sudden lunges in extreme power. with old box it was like i had a second turbo from 2500rpm+

the vac solenoid box was obviously getting stuck somewhere and not actuating the turbo arm enough and then suddenly it would realize i needed power and a woosh of air would go through and also give me the error code.

Agents= R4100 incl
Scrapyard= R1000 incl

I wonder what this will do to fuel consumption now that its boosting correctly...

Howsit bud. Where exactly did u get the vacuum box from at that price?

Howsit bud. Where exactly did u get the vacuum box from at that price?

Tricor in Port Elizabeth. 041 581 6996. Excellent guys who work there. they are a family business. Speak to David.

Just want to say thanks for the post, having similar issues (Golf 5 1.9 PD) and just beginning to delve into the problem. Checked the vanes and they move freely. Will certainly bear this in mind and check for unusual movement on the actuator.