VW T4: Performance Issues & Solutions

Hello everyone.

I've already used the search function and read several articles on the topic, but unfortunately, that hasn't helped me.

The following problem:

My T4, with engine code AUF and automatic transmission, has the following error code stored:

Thursday, July 10, 2008, 12:52:09:35547
VAG-COM Version: RKS 704.1

Address 01: Engine
Control unit part number: 074 906 018 AL.
Component and/or version: 2.5L R5 EDC 0000AG 3906.
Encoding: 00001
Workshop Number: WSC 02743.
Extended information: WV1ZZZ70Z2H060215 VWZ1Z0A1806749
"One error found:"

17965 - Turbocharger pressure control: Limit exceeded.
P1557 - 35-00 - -

Readiness: not available.

"I've already replaced all the vacuum hoses and the N75 and N18 valves. For a short time, it ran with full power again. But on the highway, it immediately lost power again. Now, I've discovered in the extended diagnostic data that the 'intake manifold pressure' is always at 2539.8, regardless of whether the car is idling, under partial load, or full load. That can't be normal, right?"
Soll ich jetzt noch den Saugrohr-Drucksensor ersetzen? What do you think?

Best regards,