M4's Rough Running Points to Critical Timing Chain Issue

Hey there! I had similar symptoms with my 2015 BMW M3 last year. The metallic noise and power loss turned out to be a failing crankshaft position sensor. Started with occasional rough idles, then progressed to power loss and higher fuel consumption. Got it diagnosed at the shop, and the sensor was indeed defective, causing timing issues. The repair wasn't too complex, but it's definitely not something to ignore. The faulty sensor can mess with your engine timing and potentially cause more serious damage if left unchecked. In my case, they replaced the sensor and cleared the ECU codes. The car ran perfectly afterward, power came back, fuel consumption normalized, and that annoying metallic sound disappeared. Took about half a day at the garage. Based on your symptoms, I'd strongly suggest getting it checked soon. It's not the most serious issue if caught early, but waiting too long could lead to bigger problems. Hope this helps.

Yeah that's exactly what happened to my M4 too! The symptoms match perfectly, same timing problems and that annoying metallic sound. I also replaced the crankshaft position sensor and it sorted everything right out. The car's been running like a dream since then. Just wondering, do you remember roughly how much you paid for the fix? And has everything been running smoothly since, or have you noticed any other quirks? Been a bit paranoid about every little noise since my experience!

Hey again! Great to hear you got it sorted with the same fix! Yeah, in my case it cost me 340 € to get that crankshaft sensor replaced. Since the repair, my M3's been running absolutely perfect, honestly, it's like a completely different car. The mechanic also managed to fix the Crankshaft to camshaft reference value that was causing those timing issues. The best part is all those annoying symptoms disappeared completely, no more weird noises, power's back to normal, and fuel consumption is what it should be. I totally get being paranoid about every little sound after something like this (been there!), but I can tell you I haven't had a single issue since the repair, and it's been over a year now. Trust me, once that sensor's replaced properly and the timing's sorted, you shouldn't have anything to worry about. These M engines are pretty solid when everything's working as it should. Just keep up with regular maintenance and you'll be fine! Let me know if you notice anything else unusual, but I bet you'll be just as happy with the fix as I was.

Thanks for sharing your experience! Actually, just got back from the mechanic yesterday. What a relief, they fixed it for around 400 bucks, which wasn't as bad as I expected. The new mechanic I found was way better than my last one, really knew their stuff about M series cars. They checked everything while they were at it and confirmed no other issues. The engine's purring like a kitten now. Such a difference in performance, it's back to being the beast it should be! Fuel consumption's normal again too, which is a nice bonus for my wallet. Funny how we both had the exact same problem. Makes me feel better knowing it's a common issue that's easily fixed. Thanks again for the help, definitely saved me some sleepless nights worrying about it. Think I'll stick with this new mechanic from now on, they really knew their stuff!