BMW M3 Boost Whistle Signals Hidden Sensor Troubles

I had nearly identical issues with my 2012 BMW M5 last month. The symptoms matched yours exactly, reduced power, whistling noise turning into a hiss, and check engine light. Turns out it was indeed the charge air temperature sensor, but the main problem was actually a loose connection at the sensor plug. The mechanic showed me that the wiring harness had some wear, causing intermittent connection issues. They had to replace the sensor connector and secure the wiring properly. The fix itself wasn't too complex, but leaving it unchecked could have led to bigger problems with the engine management system. My advice, get it checked soon. While it's not immediately dangerous to drive, running with incorrect air temp readings can affect engine performance and efficiency. The repair was pretty straightforward and took about an hour of labor.

Thanks for sharing your experience! It's really helpful to know it was the sensor and wiring in your case. Did you remember roughly how much the whole fix cost you? Been a couple weeks since your post, so curious if everything's still running smoothly or if you've noticed anything else come up? My M3's booked in for next week, and I'm trying to get an idea of what I'm in for.

Hey again! Just wanted to follow up. Yes, everything has been running perfectly since the repair, no more whistling, full power restored, and the check engine light hasn't come back. Total cost was 95 € to fix the faulty cable connection at the charge air temp sensor. The mechanic found that the connector was loose and slightly damaged, causing those intermittent connection problems we talked about. My M5 is now performing like it should, smooth acceleration, no weird noises, and the engine management system is happy. It was definitely worth getting it sorted quickly. Good call booking your M3 in, sounds like you might be dealing with the same thing. The fix was way simpler and cheaper than I initially feared. Let us know how it goes with yours next week!

Just got back from the mechanic and wanted to update everyone. The experience was actually much better than my previous shop visits! Initially, I was worried it would cost a fortune, but turns out I needed a simple fix like yours. The mechanic found a cracked vacuum hose causing the whistling sound and a worn-out sensor connector. Got both replaced, and the whole thing only cost me about 120 bucks with parts and labor. They even showed me exactly what was wrong and explained everything clearly. What a relief it wasn't something major! The car's running beautifully now, no more weird noises, full power is back, and that annoying check engine light is finally off. Really glad I didn't put this off any longer. Thanks again for sharing your experience, it gave me the push I needed to get it sorted before it turned into something worse.