My PD130 ASZ has been off the road for years but following several months of hard toil it's back on the road and I've the inevitable teething problems to sort out.
I had to free up the VNT and replace the vacuum actuator, then loads of fiddling to adjust the actuator rod to within tolerances using VCDS. Now it's working much better, although today for some reason it triggered limp mode when going up a long slope on the motorway, which in turn triggered the 17964 Charge Pressure Control Negative Deviation error code.
I'm also getting a really high pitched whistling noise as I go through 3000 revs which sounds as if it's coming from behind the dashboard. I'm wondering whether these issues are related, I can't see any evidence of leaks though and all the vacuum pipes look ok. I've searched here but can't find anything similar, any suggestions? Do the N75 valves make a whistling noise when they start going wrong?
Many thanks for any advice.