BMW 3 Diesel Running Rough? QDC Issues & Solutions Here

Hey there! I have some experience working on cars and faced something very similar with my 2019 BMW 5 Series diesel last year. When my car showed those exact symptoms, rough running, misfires, and the dreaded check engine light, it turned out to be a faulty injector. Had to get it replaced at my local workshop and it set me back about 515 Euro, but it fixed the problem completely. The 3 and 5 Series share quite a few components in their diesel variants, so it could be the same issue. Could you share your exact engine code and mileage? Also, when did these symptoms first start? This would help me give you more specific advice based on my experience. Feel free to ask any other questions. I know how annoying these issues can be, especially with modern diesel engines.

Thanks for sharing your experience! My BMW just hit 168537 KM and had its last service about two months ago. The symptoms started showing up about a week ago, getting progressively worse. Your injector theory makes sense, I've been noticing the rough idle especially when the engine is cold. The weird thing is that my mechanic replaced the fuel filter during the last service, but the problem still developed. Did you notice any specific patterns with your injector issue, like worse performance during cold starts or at specific RPMs? Just trying to confirm if I'm dealing with the same thing before booking a workshop visit.

Hey again! Thanks for those additional details. Your symptoms are sounding more and more like what I experienced with my 5 Series. Yes, actually, I had very similar patterns! The cold starts were definitely the worst, and the rough idle was really noticeable until the engine warmed up. In my case, the new fuel filter didn't help either, which initially threw my mechanic off track. The interesting thing is that my issues also started showing up gradually over about a week or two. One thing I noticed with my car was that the roughness was particularly bad between 1,500 and 2,000 RPM, it would sort of hesitate and shake a bit. The performance would improve somewhat when the engine was fully warm, but never completely went away until I got the injector replaced. Given your mileage and symptoms, I'd put money on it being an injector issue. These modern diesel injection systems are super sensitive, and even a slightly faulty injector can cause all sorts of problems. When I finally got mine sorted, the mechanic showed me the diagnostic readings, and the quantity drift compensation values were way off on one cylinder. Since you're experiencing such similar symptoms, I'd definitely recommend getting those injectors checked out. Better to catch it early before it potentially causes more issues.

Thanks so much for the detailed follow-up! It's incredible how similar our issues sound, especially that rough running between 1,500 and 2,000 RPM. I've been noticing exactly the same thing! And you're spot on about the symptoms being worse during cold starts and improving slightly when warm. I've just booked an appointment with my mechanic for next week. After hearing about your experience, I'm pretty convinced it's an injector problem too. The fact that both our cars showed the same gradual onset of symptoms, and that the fuel filter replacement didn't help, really seals it for me. Quick question, after you got the injector replaced, did you notice any immediate improvement in performance? And did you have to get any additional parts replaced along with it? Just want to be prepared for what might be coming cost-wise. Really appreciate you taking the time to share your experience. It's been super helpful in narrowing down what's likely wrong with my car!