M2 Engine Trouble: Limp Mode and Failed Emissions Test

Hey there! I had very similar issues with my 2020 BMW M4 last winter. The symptoms you're describing sound exactly like what I experienced, rough running, limp mode, and failed emissions. Turned out I had a significant exhaust leak at the manifold-to-downpipe connection, and two of the gaskets had completely deteriorated. Found a good specialist who diagnosed it with a smoke test. They had to replace the gaskets, two damaged studs, and a small section of the downpipe that had warped from heat. It was a pretty serious issue that needed immediate attention since it was affecting engine performance and could've led to more expensive problems if left unchecked. The repair took about two days, but the car's been running perfectly since then, smooth power delivery, no check engine light, and passed emissions with flying colors. Make sure whoever looks at it has specific experience with BMW M engines. The S55/S58 motors have their quirks, and you want someone who knows what they're doing. Best of luck with the repair.

Thanks for sharing your experience! Sounds spot on similar to my issue. This really helps narrow down what might be wrong with my M2. Really glad to hear you got it sorted out properly. Quick question, do you remember roughly how much the whole repair set you back? Also, has everything stayed running smoothly since the fix, or have you noticed any other issues pop up?

Hey again! Happy to help follow up! The repair cost me 265 € total, which was actually less than I expected given how serious the exhaust leak was. And I've got great news, since getting it fixed last winter, the car's been running absolutely perfect. No more uneven engine running, no check engine lights, nothing. It's like a completely different car compared to how it was running before. The mechanic really knew their stuff with these M engines. Money well spent if you ask me, especially since I was worried it might've been something much more expensive. The smooth running and proper performance are totally worth it. I've put quite a few kilometers on it since the repair and haven't had a single issue pop up. Goes to show how one problem can really affect the whole system, but once you get it properly diagnosed and fixed, these engines are solid. Just make sure whoever looks at yours knows BMW M cars specifically, it makes all the difference. Feel free to ask if you need any other details about the repair!

Thanks so much for all the details! I finally got my act together and took my M2 to a specialist mechanic yesterday. You won't believe it, it was exactly what you described! Had a nasty exhaust leak that was causing all the problems. The repair bill came in at around 300, which honestly feels like a bargain considering how worried I was. The mechanic was fantastic, really knew their stuff and walked me through everything they found. Such a relief after my last disappointing mechanic experience. Took it for a proper drive this morning and what a difference! No more rough running, check engine light's gone, and it pulls like it should again. Feels like I've got my old car back. Really glad I asked here and got your advice, saved me from probably making things worse by putting it off any longer. Thanks again for helping me sort this out. Nothing beats getting advice from someone who's been through the same thing!