BMW Z3 Boost Issue: Sensor Fault or Bigger Problem?

Hey there! I had a somewhat similar issue with my 1998 BMW Z4 last year, and I'd consider myself to have some experience working on cars. That whistling sound with power loss rings a bell. Mine turned out to be a faulty connection in the charge air temp sensor wiring, basically, the plug was corroded and not making proper contact. Took it to my regular workshop, and they diagnosed it pretty quickly. The total fix was around 95 Euro, mostly labor costs for cleaning connections and replacing a damaged cable. Before jumping to conclusions though, I'd need to know: Have you noticed any other symptoms? What's your mileage? Is the whistling constant or only under specific conditions? If you're interested, I can share more details about my repair process. These issues on the Z series can be tricky, but they're usually not catastrophic. The Z3 and Z4 share quite a few similar components in this area.

Thanks for the response! Yeah, my Z3 is at 152424 KM and just had its service last month. The whistling only happens during acceleration, and it gets louder as I push the pedal harder. Haven't noticed any other symptoms besides the power loss and that annoying sound. Your experience with the sensor wiring sounds promising, definitely cheaper than what I was worried it might be! Would love to hear more about your repair process, especially since these Z series cars seem to have similar quirks. Did you try any troubleshooting before taking it to the shop?

Hey again! Thanks for those details about your Z3. You know, when I had this issue with my Z4, I actually did try some basic troubleshooting before taking it to the shop, thought I might save some cash. First thing I did was check all the visible connections around the charge air temp sensor, just gave them a visual inspection and tried wiggling them a bit to see if the sound changed. In my case, I found the whistling was also rpm-dependent, louder with higher revs, just like yours. Given your mileage is pretty close to what mine was (mine was around 160000 KM when this happened), I'm even more convinced it could be the same issue. Quick funny story, I actually drove around for about two weeks making that weird whistling noise before getting it fixed. My neighbor thought I'd installed some kind of fancy turbo mod! But seriously, don't wait as long as I did. When I finally got it sorted, the mechanic showed me how the corroded connection was actually starting to damage the sensor itself. If I'd waited longer, I would've needed to replace the whole sensor unit instead of just fixing the wiring. Since you just had service done, check if they might have disturbed any connections while working on something else, sometimes these things can get knocked loose during routine maintenance. Let me know what you find, and I can share more specific details about what my repair involved if you're interested in going the DIY route.

Thanks so much for all that detailed info! That's super helpful, especially knowing yours made the same rpm-dependent whistling sound. Actually, now that you mention it, the timing of this issue is interesting since it started pretty soon after that service. I'll definitely check those connections first, maybe something did get knocked loose during maintenance. That story about your neighbor thinking it was a turbo mod made me laugh! I've been getting some weird looks at traffic lights too. But you're right, I should probably get this sorted soon before it potentially damages the sensor. I might take a look at those connections myself this weekend, and if I can't spot anything obvious, I'll get it to a shop next week. Really appreciate you taking the time to share your experience, definitely makes me feel better knowing it might just be a relatively simple fix rather than something major. I'll let you know what I find when I check those connections!