BMW 4 Diesel Acting Up, Power Loss & Engine Jerking

Hi there! I've got some experience dealing with cars (low experience, mostly basic maintenance). Had a similar issue with my 2018 BMW 3 series diesel last year. The symptoms you're describing sound exactly like what I went through after getting a chip tune from a third-party shop. My car was jerking badly and lost power, felt like it was in limp mode. Took it to my regular workshop, and they found that the tune was causing conflicts with the engine management system. Had to get it reset to factory settings and do some ECU recalibration. Cost me around 180 Euro but sorted the problem completely. Before I can help more specifically: Could you share if you've had any recent modifications done to your car? Also, what's the exact fault code you're getting? Would help narrow down if we're dealing with the same issue. PS: Love these 4 series BMWs! Was actually considering upgrading my 3 series to one.

Thanks for sharing your experience! No mods on my car at all, it's completely stock. Just did my regular service two months ago at 131456 KM. The fault code showing is P0299, and the jerking seems worse during acceleration. Actually, the symptoms started right after a long motorway drive. Really interested in what you mentioned about the ECU. Did your car also have any issues with black smoke or turbo noise before you got it fixed? Just trying to figure out if I should expect a similar fix or if I'm looking at something different here.

Hey again! Oh P0299, that's a different story from what I dealt with! Now that you mention the symptoms starting after a highway drive, plus the black smoke question, this is ringing some serious turbo-related bells for me. When my 3 series had the tune issue I mentioned before, I actually ended up having a follow-up problem a few months later with similar symptoms but different cause. Turned out to be a failing turbocharger. The P0299 code (turbo underboost) showed up, and I was getting that exact same jerking during acceleration. In my case, there was a small boost leak from a cracked intercooler pipe, way cheaper fix than I initially feared. Check for any loose connections or damaged hoses around your turbo system. Mine actually made a slight whistling noise when accelerating before it was fixed. Since you're stock and recently serviced, I'd bet money you're looking at either a boost leak or maybe a wastegate issue. My fix was about 400 Euro including parts and labor, way better than the 2000+ I was worried I'd need for a full turbo replacement! Let me know what you find out. These diesel turbos can be tricky, but usually it's not as bad as it first seems.

Thanks so much for the detailed follow-up! You've really eased my mind about this. I've been worried sick thinking I'd need to replace the entire turbo unit. Just checked under the hood and actually noticed a slight hissing sound near the intercooler area when revving, might be that boost leak you mentioned. Going to get it to my mechanic tomorrow morning. Really hoping it's just a cracked pipe like in your case. The symptoms match exactly what you described, especially that jerking during acceleration. Will definitely update once I know what's going on. Quick question though, after your repair, did you notice an immediate improvement in performance? Just want to know what to expect if it turns out to be the same issue. Thanks again for all the help. Really appreciate you taking the time to share your experience in such detail!