BMW Z4 Engine Woes: Limp Mode and Smoke Issues

Hey there! I had a pretty similar issue with my 2004 BMW Z3 last year (and I also own an E46). I'd say I have some experience working on cars, though I'm no pro mechanic. Those symptoms sound really familiar. My Z3 was doing the same thing, limping, jerking, and smoking. Turned out it was carbon buildup in the combustion chambers causing pre-ignition issues. Took it to my regular workshop and they did a thorough cleaning of the chambers, replaced some sensors, and it ran like new afterward. The whole thing cost me around 425 Euro, but it was worth every penny. Before I can give more specific advice, could you share: How many miles/kilometers are on your Z4? What type of fuel do you usually use? When was the last time you had any major engine work done? This info would help me understand if you're dealing with the same problem I had.

Thanks for the detailed response! My Z4 has 69222 KM on the clock, and the last service was about two months ago. I typically use premium fuel only. What's interesting is that my symptoms match exactly what you described with your Z3. The smoking and jerking started pretty suddenly, maybe a week ago. I'm actually relieved to hear that your issue was resolved with a thorough cleaning and sensor replacement rather than something more serious. Did you notice any warning lights on the dash before taking it in? I'm seeing a check engine light that keeps coming on and off.

Hey again! Yes, those warning lights were definitely part of my experience too with the Z3. The check engine light was playing that exact same on-off game with me, super annoying! With similar mileage to yours, it's making even more sense now that we're probably looking at the same issue. Just thinking back to my situation, the smoking was particularly noticeable when I would accelerate hard, right? That's actually what pushed me to get it checked out sooner rather than later. The jerking was really unpredictable too, sometimes barely noticeable and other times feeling like the car was having a fit. Since you're using premium fuel like I was, I'm even more convinced it's that carbon buildup issue. After they cleaned mine out, the difference was like night and day. The workshop also found that my oxygen sensor was a bit wonky, which was contributing to the whole mess. They replaced that along with doing the carbon cleaning. Quick tip from my experience, if you do take it in, ask them to check the ignition coils while they're at it. Mine were fine, but the mechanic said these symptoms can sometimes be related to failing coils too. Better to check everything while they're in there, you know? The repair totally sorted out my Z3, and it's been running smooth as butter since then. Let me know what you end up finding out, I'm curious if it turns out to be the same problem!

Thanks so much for all that helpful info! You're right, the smoking is definitely worse during hard acceleration, and the jerking is exactly as unpredictable as you described. It's actually a huge relief to hear that your Z3 had such similar symptoms and it wasn't something catastrophically expensive to fix. Given how closely our situations match, similar mileage, same fuel type, and identical symptoms, I'm feeling pretty confident now that I'm dealing with the same carbon buildup issue. I'll definitely take your advice about getting the ignition coils checked too. Better to be thorough while they're working on it. I've already called my local BMW specialist and booked it in for next week. I'll make sure to mention the carbon cleaning and sensor check based on your experience. Really hoping it'll be a similar fix and cost to what you had. I'll probably get the oxygen sensor replaced too since that seemed to be part of your solution. Thanks again for sharing your experience, it's helped me feel much more informed about what I might be dealing with. I'll update you once I get the diagnosis and work done!