BMW 3 Diesel Power Loss: Turbo or Actuator Issue?

Hey there! I had a similar issue with my '03 BMW 5 series diesel last year. I've got some experience working on cars but this one was beyond my DIY skills. My car showed pretty much the same symptoms, power loss, weird whistling noise, and terrible fuel economy. Took it to my trusted workshop and it turned out to be the electrical bypass valve that was completely shot. Repair cost me about 250 Euro, but it solved all the issues right away. The engine runs smooth now, and the fuel consumption is back to normal. Before I can share more specific details, which 3 series do you have exactly (320d, 330d)? That would help me know if you're dealing with the exact same setup I learned about during my repair. Just a heads up, don't drive it too long with these symptoms. Could lead to more expensive problems if left unchecked.

Thanks for sharing your experience! Mine's a 320d with 27791 KM on the clock since the latest service. Those symptoms you described match mine exactly, especially that whistling noise. Good to know about the bypass valve, that could explain why my boost pressure feels off. I'll definitely get it checked out soon rather than risk any further damage. Did you notice any other warning signs before the valve completely failed?

Hey again! Yeah, now that you mention your 320d, it's definitely similar to what I experienced. Before my bypass valve completely failed, I noticed a few warning signs I didn't mention in my first reply. The whistling noise actually started pretty subtle at first, mostly noticeable during cold starts. Then it got progressively louder over about two weeks. Another thing I remembered, the car would sometimes feel really sluggish for the first 5-10 minutes of driving, especially in the morning. It's like the turbo wasn't kicking in properly. This happened maybe a week before everything went downhill. With your mileage since the last service, it's about the right time these valves start acting up. Mine failed at similar mileage actually. The good news is that fixing it early saved me from any turbo damage, which would've been way more expensive. Quick tip from my experience, when you take it to the shop, ask them to check the vacuum lines while they're at it. My mechanic found a small crack in one of those too, which wasn't helping the situation. Let me know how it goes when you get it checked out. Curious to hear if it's the same issue!

Thanks for the additional details, that's really helpful! Actually, now that you mention it, I have noticed that morning sluggishness too, especially this past week. I just figured it was normal cold weather behavior, but it makes more sense now. I've already called my mechanic and booked it in for tomorrow morning. Really appreciate the tip about checking the vacuum lines, I'll definitely mention that to them. Will let you know what they find, but seems like we might be dealing with the exact same issue. Thanks again for taking the time to share your experience, you've saved me a lot of worry about what might be wrong!