Mini Roadster Engine Issues

Sounds like you're chasing the boost gremlins! I had a similar issue with my Mini Roadster. Check your turbo actuator and wastegate. A faulty turbo actuator could cause all those symptoms, especially the whistling and hissing. It's like a leaky faucet in your boost system. Is the actuator arm moving freely?

Interesting. When you say 'actuator arm', are you talking about the rod that connects to the turbo wastegate? And how exactly did you diagnose yours? Any specific tests I should run before throwing parts at it?

Yep, that's the one. In my case, the arm was sticking and not moving smoothly. The shop confirmed it with a boost pressure test. You could try manually moving the arm with the engine off to see if it feels tight or restricted. If you're not comfortable doing that, I'd suggest getting it checked at a workshop. These turbo issues can be tricky to diagnose without the right tools.

Just wanted to close the loop on this. Turns out it was indeed the electrical bypass valve, like you suggested. Got it replaced for around 250€. Car's running like a champ again. Thanks for the insight!