BMW 8 Diesel: Power Loss & Whistling, Boost Issues?

Hey there! I have some experience working on cars and dealt with something very similar on my 2020 BMW 7 Series diesel last year. Those symptoms sound exactly like what I experienced, the whistling, power loss, and that annoying stalling at idle. Turned out my electrical bypass valve was shot, which explained all those issues. Took it to my regular workshop and they diagnosed it pretty quickly. The fix was straightforward but cost me around 250 Euro, parts and labor included. Since then, I switched to a 5 Series and haven't had any similar issues. Before jumping to conclusions though, could you share: Current mileage? When did these symptoms first appear? Any recent maintenance done? This would help confirm if we're dealing with the same problem. Feel free to share more details!

Thanks for sharing your experience! My 8 Series is at 170148 KM and just had its service last month. The symptoms started about a week ago, getting progressively worse. The whistling noise really matches what you described with your 7 Series. Good to know about the electrical bypass valve, that's actually a bit of a relief compared to what I was thinking. The price sounds reasonable too, definitely better than what I was expecting for a boost pressure actuator replacement. Did your car also have increased fuel consumption when you experienced this? Mine's been drinking fuel like crazy lately. Think I'll get it checked at the workshop you mentioned, better safe than sorry with these symptoms.

Hey again! Yeah, I remember exactly how my fuel consumption went through the roof when I had that electrical bypass valve issue with my 7 Series. It was literally drinking fuel like there was no tomorrow, pretty much like what you're describing with your 8 Series. Actually had to fill up twice as often as usual, which was a real pain. You know what's funny? I initially thought it was the boost pressure actuator too, just like you did. Even had a heated argument with my mechanic about it! But he proved me wrong, and I'm glad he did because the bypass valve repair was way cheaper. Quick heads up though, since your car's done more miles than mine had (mine was around 150K when it happened), might be worth getting them to check the surrounding components while they're at it. When they fixed mine, they noticed the turbo seals were starting to show some wear too. I got those done at the same time and it saved me another workshop visit a few months down the line. Just keep an eye on that whistling noise until you get it sorted. If it starts getting louder, might want to ease off the accelerator a bit. That's what I did, and it helped prevent any bigger issues until I could get it fixed. Let me know how it goes! Always curious to hear if others run into the same fixes I did.

Thanks so much for all this detailed info! That's super helpful, especially about the turbo seals, definitely gonna have them check those too while they're poking around. You've honestly made me feel a lot better about this whole situation. I was stressing about a massive repair bill, but this sounds much more manageable. Really appreciate you mentioning that tip about taking it easy on the accelerator if the whistling gets worse. I've been babying it a bit already, but good to know that's the right approach. Will definitely ease off more if that noise increases. I'll schedule an appointment for tomorrow and get this sorted. Thanks again for sharing your experience, saved me a lot of worry and probably some cash too! I'll let you know what they find when I get it checked out.