I already had theese problems once, so I replaced solenoid... nothing. MAF helped, but it showed on gauges as ESP SYSTEM FAULT and in diagnostic software too.

Then I got issue with oil housing (typical whistle and vacuum under oil cap). Replaced. Fixed.

Now I have again issue with boost. Gonna try replace solenoid and MAP and will see. I dont have any engine light, ESP light... or any other error.
I update info here after replacement will be done.