1.9 TDI AHF: Limp Mode Above 4000 RPM

Hello Diesel species,

I've been struggling with this problem and searching the internet for a solution for the past 4 hours, but I haven't found anything.

I have a 1999 Volkswagen Golf TDI, 81 kW, 96,000 km, engine code: AHF. It's completely stock, no modifications or tuning.

As soon as you rev the engine a few seconds above 4000 RPM, it goes into limp mode, and no lights illuminate on the instrument cluster. Turn the car off, restart it, and it runs normally again until you rev it above 4000 RPM again. The error can be reproduced at any time.

My independent mechanic read an error code that says 'boost pressure exceeded the limit.'
I then checked the VTG function, but everything seems to be working perfectly. I created a vacuum with my mouth, and the mechanism pulled evenly. Then, while the engine was idling, I alternately connected and disconnected the hose to the VTG valve to the solenoid valve, and the valve smoothly moved 1-1.5 cm and returned smoothly to its original position.

'Therefore, I can rule out soot buildup on the turbine blades, correct?'

What else could it be?

The vacuum hose from the VTG sensor to the solenoid valve is new; the others appear to be in good condition.

'I read something about a small air filter near the solenoid valve that might be clogged, or that the hose leading to it might be kinked. However, I haven't been able to find it. Does it exist? From the solenoid valve, there's one thicker hose going to the air filter housing, one to the VTG sensor, and one to a check valve (which is working).'

4. How can I test the solenoid valve? It produced a noticeable vacuum when idling.

I'm completely stuck. Unfortunately, I don't have a VAG-COM or any other diagnostic system at home. I don't want to take it to the workshop because they'll just replace parts one by one.

If any of you diesel experts happen to be in the Nuremberg or Halle/Leipzig area, feel free to stop by. I'm happy to compensate you for your time.

I appreciate any advice you can offer.

Thank you very much.
Uli.

Hello Uli,
"Please swap the control valves for the AGR (Abgasrückführung) and the turbocharger. The part numbers are different."
Although (1H0906627 or 1H0906627A), it does not impair the function in this case.

Best regards, Micha.

Hi,

Just got back from the test drive. Unfortunately, even with the swapped solenoid valves, the same problem persists: it's in limp mode.

CRAP!

'Thank you for the tip, nonetheless.'

Anyone else have any ideas?

Diagnosis
Anything else really won't get you very far.

Best regards, Micha.