V50 boost pressure issue

I had similar symptoms on my Saab 9-3. It turned out to be a vacuum leak affecting the turbocharger. Have you checked for any hissing sounds, especially around the hoses connected to the boost pressure control system? Compressor surge is also a possibility.

Thanks for the Saab 9-3 info. I'll check for vacuum leaks. Can you give me more details about where you found the leak?

The vacuum leak was a small, almost invisible crack in the hose connected to the bypass valve actuator. Check carefully, but a workshop might have tools to test each part of the system.

Thanks! I took your advice and went to a workshop. It was the vacuum switching valve. Replacing it cost 140€ and fixed the boost pressure issue.