BMW Z3 Jerking with Smoke: Knock Sensor or Engine Crisis?

Hey there! I had a similar issue with my '98 BMW M3 last year. I have some experience working on cars, but this one was beyond my DIY skills. My car showed the same symptoms, jerking, limp mode, and that annoying smoke. Turned out to be carbon deposits in the combustion chamber. Had to take it to a workshop where they did a thorough cleaning of the chamber and valves. Cost me around 425 Euro, but it fixed the issue completely. What's your mileage and maintenance history? Also, which engine variant does your Z3 have? This info would help me share more specific details about what to look out for.

Thanks for sharing your experience! Mine's at 95961 KM and just had its service last month. The smoke and jerking started about a week ago, and it's getting worse. I was hoping it wouldn't be the combustion chamber, but your description matches my symptoms perfectly. I've got the 2.8L engine, and it's been running like a dream until now. Did your mechanic mention how long the cleaning process took? Also wondering if they found any other issues while they were in there. Really appreciate the help!

Hey again! Yeah, I totally get your concern. When my M3 had these issues, the cleaning process took about 6-7 hours. The mechanic actually found some worn-out spark plugs while doing the job, so I had those replaced too. The carbon build-up was pretty bad, especially around the intake valves. For reference, my car had around 110,000 KM when this happened. The 2.8L engine in your Z3 is quite similar to what I had, and these symptoms are pretty typical for BMWs of our era. The carbon deposits tend to build up even with regular maintenance, it's just one of those things with these engines. One thing I forgot to mention in my first response, after the cleaning, my mechanic recommended using a fuel system cleaner every few thousand kilometers to help prevent future build-up. Been doing that religiously since then, and haven't had any issues for the past year. Just make sure you get it checked soon though. I waited a bit too long and ended up with slightly scored cylinder walls, which added to the repair cost. Better to catch it early! Let me know how it goes after you get it looked at. These old BMWs are worth the hassle though, still love mine to bits!

Thanks so much for all this detailed info! Hearing about your experience definitely makes me feel better about what I'm dealing with. I'll call my mechanic first thing tomorrow and mention the carbon deposit issue. Really good to know about the timing too, 6-7 hours isn't as bad as I feared. I'll definitely ask them to check the spark plugs while they're at it. Can't believe I didn't think about those! That's a great tip about the fuel system cleaner. I'll pick some up once this is sorted. Better to prevent future problems than deal with another headache like this. Really don't want to risk any cylinder wall damage! You're absolutely right about these old BMWs being worth the trouble. Even with this issue, I still love my Z3, just want to get her running smoothly again. I'll update you once I get it sorted. Really appreciate all your help and advice!