BMW 3-Series Running Rough: Common Causes Revealed

Hey there! I have some experience working on cars and went through something very similar with my '07 BMW 5-series last year. The symptoms you're describing sound exactly like what I experienced. In my case, it turned out to be a nasty leak in the exhaust system that was messing with the oxygen sensors. Had my usual workshop check it out, they found cracks around the manifold area. Got it fixed for about 265 Euro and the car's been running smooth since then. Before I share more specifics, could you tell me your mileage and if you've noticed any unusual exhaust sounds or smells? Also, are you getting any specific error codes? That would help narrow things down. The 3-series and 5-series are pretty similar in their setup, so I might be able to point you in the right direction once I know more details.

Thanks for sharing your experience! I've got 83831 KM on the clock and just had a service done last month. No unusual exhaust sounds that I've noticed, but I'm getting the P0300 unusual misfire code along with P0303 for cylinder 3. The car runs fine when cold but starts acting up after warming up. Could your exhaust leak have caused similar codes? Just wondering if I should check that first before digging deeper into ignition components.

Hey again! Thanks for those details, actually, my situation was a bit different when I look at your codes. While I did have the exhaust leak I mentioned, those specific misfire codes you're getting remind me of another issue I had with my BMW before that. Around 90000 KM, I had almost identical symptoms, rough running when warm, misfires, and similar codes. Turned out my ignition coils were shot, particularly on cylinder 3. Had the spark plugs checked too while they were at it, they were pretty worn. Replaced all coils and plugs as a set and it solved the problem completely. Since you mentioned it runs fine when cold but acts up when warm, that's really typical of failing coils. They tend to break down as they heat up. My repair bill was about 400 for parts and labor, but it was totally worth it. The car ran like new afterward. If I were you, I'd definitely check the ignition components before looking at exhaust issues. Those P0300 and P0303 codes are pretty much pointing straight at ignition problems. Want me to share what brand of coils I used? They've been holding up great for the past year.

Thanks so much for the detailed explanation! That's really helpful, especially since you've dealt with both issues. You're right, the symptoms matching up with the coil failure makes a lot more sense than an exhaust leak, especially with those specific codes. Would definitely appreciate knowing which coil brand you used! I'll get the coils and plugs checked first. Actually feeling kind of relieved now, I was worried it might be something way more expensive like fuel injectors or internal engine problems. Will probably just go ahead and replace all the coils and plugs while I'm at it since they're probably all about the same age anyway. Really appreciate you taking the time to share your experience. Will update the thread once I get it sorted out in case anyone else runs into the same issue!