BMW M4 Rough Running & Stalling: Ignition Coil Issue?

Hi there! I had a somewhat similar issue with my 2014 BMW M3 last year, and I have some experience working on cars (though I'm not a pro mechanic). My car showed almost identical symptoms, rough running, jerking, and that annoying check engine light. It turned out to be a loose connection in the wiring harness to one of the ignition coils. Took it to my regular workshop, and they diagnosed it pretty quickly. They found that the plug connection was worn and not making proper contact. The fix involved replacing the damaged wiring and connector, which cost me about 95 Euro. Car's been running smooth since then. Could be something similar in your case, but to help you better, could you share: Current mileage on your M4? Does the problem occur more when the engine is cold or warm? Have you scanned for error codes? Let me know these details and I might be able to offer more specific advice based on my experience with BMW engines.

Thanks for your detailed response! My M4 has 24952 KM on the clock, and the last service was just done recently. The problem actually happens more when the engine is warm, especially after driving for about 15-20 minutes. Haven't scanned for codes yet, but planning to do that tomorrow. Your experience with the wiring harness issue is really helpful, might be worth checking that too. Did your car also have any misfire symptoms? The repair cost you mentioned seems reasonable if it turns out to be something similar.

Hey again! Yeah, my M3 actually did have misfire symptoms too, especially during warm conditions just like you're describing. When the engine was at operating temperature, it would misfire and run really rough. The reason I initially thought it was just the ignition coil itself was because these symptoms are so similar. But after my mechanic found that loose connection in my wiring harness, it made total sense. The heat from the engine was probably making the already loose connection even worse, which explains why the problems got more noticeable when warm. Just a heads up though, in my case, the initial diagnosis of a bad ignition coil wasn't completely wrong. After fixing the wiring, we found that the connection issues had actually damaged one of the coils too. Ended up replacing that as well, which added another 120 Euro to the bill. Still way cheaper than replacing all the coils blindly! Definitely get those codes read first. That'll give you a much better starting point. If you're getting misfire codes for a specific cylinder, it'll make tracking down the issue much easier. My bet would be on either a wiring issue like mine or a legitimately failed coil, both of which are pretty straightforward fixes. Let me know what the scan shows up. Would be interesting to see if it's the same problem I had!

Thanks so much for sharing all those details! That's really interesting about how the heat made your connection issues worse, it sounds exactly like what I'm experiencing. You're right, I should definitely get those codes read first before jumping to conclusions about the ignition coils. The fact that you had both wiring and coil issues is super helpful to know. I'll make sure to have them check both when I take it in. Around 215 Euro total for your repair doesn't sound too bad at all, I was worried it might be something much more expensive. I'll get those codes scanned tomorrow and will probably have my mechanic take a look at the wiring harness first, following your experience. Really appreciate you taking the time to explain everything in such detail. Will keep you posted about what they find, fingers crossed it's as straightforward as your repair was!