BMW M4 Engine Issues: Knock Sensor Troubleshooting Help

Hey there! Had similar issues with my 2017 BMW M3 last year. Those symptoms match what I experienced, rough running, sluggish acceleration, and increased fuel consumption. Initially thought it was the knock sensor too, but turned out to be a failed ignition coil and a couple of worn spark plugs. The technician found that the connector on one of the coil packs was corroded, causing intermittent connection issues. It wasn't a major repair job, but definitely needed immediate attention to prevent potential engine damage. Got all coils and plugs replaced as a set since they tend to wear at similar rates. If you're concerned about your mechanic, get a diagnostic scan first, this will point to whether it's actually the knock sensor or something else. These symptoms can be caused by various issues, and it's worth getting the proper diagnosis before replacing parts.

Thanks for sharing your experience! That's really helpful, my symptoms do sound exactly like what you described. I'm thinking I should definitely get those coils and plugs checked out first before jumping to conclusions about the knock sensor. Would you mind telling me roughly what you ended up paying for the repair? Also curious if you've had any similar issues pop up since getting it fixed? Cheers

Hey there! Actually, I need to correct my earlier response, in my case, it did turn out to be the knock sensor after all, not the coils and plugs as I initially thought. Just got it fixed last week and it's running like a charm now! The mechanic found that the cable connection to the knock sensor was faulty, causing all those symptoms we discussed. The repair was surprisingly straightforward and cost me 95€, much less than I was expecting. Since the fix, my M3 is back to its old self, smooth acceleration, normal fuel consumption, and no more check engine light. No issues whatsoever since then. Sorry for misleading you earlier about the coils and plugs! Sometimes these symptoms can be tricky to diagnose, but in my case, it really was the knock sensor. If you're experiencing the same issues, definitely worth getting it checked out, might save you some headache and money in the long run. Let me know how it goes with yours!

Just wanted to give you an update on my M4 situation. Finally got it checked out at a different mechanic, and you won't believe it, it was actually a combination of issues! The main culprit was indeed a faulty knock sensor, but they also found a loose wiring connection that was causing some of the problems. The repair was pretty reasonable, around 130 bucks total. The mechanic explained everything clearly and even showed me the old parts. What a relief to have found an honest professional! The car's running beautifully now, no more rough idling or acceleration problems. Thanks again for sharing your experience. It really helped me build up the confidence to get this sorted out. Definitely keeping this mechanic's number for future reference! Take care!