BMW 1 Series Diesel: Multiple Issues Point to Boost Fault

Hey there! I've got some experience working on cars and had a very similar issue with my 2011 BMW 3 diesel (320d). Those symptoms sound really familiar, I dealt with exactly the same problems on mine last year. After struggling with it for a couple weeks, I took it to my regular workshop. They diagnosed it as a faulty electrical bypass valve, basically the same component you're suspecting. The whole repair, including parts and labor, cost me about 250 Euro. Since getting it fixed, the car's been running perfectly again, no more power loss or weird noises. Before I share more specific details about my repair experience, could you tell me your exact engine variant and current mileage? That would help me give you more relevant advice since BMW has a few different diesel engines in the 1 series. Just a heads up, if it is the bypass valve, don't wait too long to get it checked. Driving with this issue can potentially cause more expensive problems down the line.

Thanks for the detailed response! I've got the 118d with 23010 KM on it, and I just had it serviced last month. After reading your experience, I'm pretty convinced it's the bypass valve, the symptoms match exactly what I'm experiencing. It's reassuring to hear the repair wasn't too expensive in your case. I'll definitely get it checked out soon to avoid any further damage. Did you notice any warning signs before the valve completely failed?

Hey again! Yeah, with your 118d, it's definitely sounding more and more like the bypass valve issue I had with my 320d. Actually, before it completely failed on my car, I did notice some early warning signs that I probably should've paid more attention to. About a month before things got really bad, I started noticing this slight whistling sound when accelerating, but only when the engine was cold. It was pretty subtle at first, I actually thought I was imagining it. Then it started getting more noticeable, especially during morning starts. The fuel consumption crept up gradually too. I remember checking my average consumption and thinking "this seems a bit high" but didn't make the connection at first. Mine was about 2 liters per 100km more than usual before I got it fixed. One thing I forgot to mention in my first response, the check engine light on mine was intermittent at first. It would come on for a few days, then go off, which made me think it wasn't too serious. Big mistake! When it finally started affecting the power output, that's when I knew I couldn't ignore it anymore. Since you've got relatively low mileage, you might be able to get this covered under warranty. Definitely worth checking that out before paying for repairs. Just make sure to get it sorted soon, I learned the hard way that these issues don't fix themselves!

Thanks so much for sharing those details about the warning signs, that's really helpful! What you described about the cold start whistling and gradual fuel consumption increase is exactly what I've been experiencing. I actually hadn't thought about the warranty angle, that's a great suggestion since my mileage is still pretty low. I just checked my warranty paperwork and I might still be covered. I'll call the dealership tomorrow to check on that before taking it to my regular workshop. You've definitely helped me feel more confident about what I'm dealing with here. I'll get it sorted right away rather than waiting for it to get worse like I was tempted to do. Thanks again for taking the time to share your experience!