Solenoid Valve: Troubleshooting Performance Loss

Hello everyone,

Does anyone know the exact function of the solenoid valve?
above the LLM (Low-Level Module) on a Passat (PD, 85 kW, model year 2000).
is attached on the left side?
I suspect that this valve is the cause of the performance loss we've been searching for.
The part has an electrical connector and two hose connections.
It appears to be responsible for the pressure bypass that controls the turbocharger.

Problem: Intermittent power loss; the workshop, as usual, is unable to diagnose the issue.
I can imagine that the device occasionally just outputs its maximum power, which can result in acceleration delays and, sometimes, a reduced top speed.

So long .
Thorsten.