BMW M2 Engine Knocking Crisis: Limp Mode and Power Loss

I had similar issues with my 2018 BMW M4 last year. The symptoms were nearly identical, power loss, jerking, and smoke under acceleration. Turned out to be carbon buildup in the combustion chamber causing pre-ignition and knock. Had to get a complete carbon cleaning service done. The mechanic showed me the deposits they removed, pretty shocking amount for a performance engine. The job involved removing the intake manifold and walnut blasting the valves and chamber. Also replaced spark plugs since they were affected. Wasn't a quick fix but solved the problems completely. Performance came back to normal and the engine runs smooth now. This is a known issue with direct injection engines. Not super serious if caught early, but can cause bigger problems if ignored. Regular maintenance with high-quality fuel and occasional Italian tune-ups (high RPM runs) help prevent buildup.

Thanks for sharing your experience! That sounds exactly like what I'm dealing with. The carbon buildup explanation makes total sense with those symptoms. Really glad to hear you got it sorted out. Quick question, do you remember roughly what the carbon cleaning service set you back? Also, has everything stayed running smoothly since the fix, or have you noticed any other quirks pop up? Trying to get an idea of what I'm in for with this repair.

Hey again! Since we last talked, I actually went ahead and got my M4 fixed for those exact issues. The cleanup service cost me 425 € and honestly, it was worth every penny. The knocking problem completely disappeared and my car's running like a dream now, no more jerking or smoke clouds when I hit the gas! The mechanic did a thorough job cleaning out all those carbon deposits in the combustion chamber. It's been about 6 months since the fix, and I haven't had a single problem pop up. The engine's purring like it should, and the power's back to what you'd expect from an M4. Just keep in mind that with these direct injection engines, you'll probably need to do this service again in the future, it's just part of owning these cars. I'm now being extra careful about using top-tier fuel and giving the engine a good run now and then to help prevent buildup. But yeah, definitely get it sorted, your M2 will thank you for it!

Really appreciate the detailed follow-up! You've honestly made me feel much better about getting this fixed. Called a mechanic today and booked my car in for next week. Had a pretty frustrating experience at another shop where they kept the car for three days and couldn't figure out the problem. This new place seems much more knowledgeable though. The guy I spoke with immediately suspected carbon buildup when I described the symptoms, just like you mentioned. He even walked me through their cleaning process. Quoted me slightly more than what you paid, but still seems reasonable considering the specialized work. After dealing with the jerky acceleration and reduced power for weeks, I can't wait to get my M2 back to its proper form. Think I'll start following your maintenance tips too, premium fuel and regular high-rev runs sound like smart preventive measures. Thanks again for all your help with this!