BMW M3 Rough Idle Mystery: Bad Mount or Something Else?

Hi there! I've had some experience working on BMWs. I actually faced a similar issue with my 2019 BMW M4 last year. The symptoms you're describing sound really familiar. In my case, it turned out to be a loose connector on one of the ignition coils. The workshop found that the cable connection was defective, causing misfires which led to those vibrations and rough idle you mentioned. Got it fixed for around 95 Euro, mainly labor costs since they just needed to replace the connection. Before jumping to engine mount conclusions, I'd suggest getting those error codes read. Which error code you're getting? Does the vibration change with RPM? Is the check engine light steady or flashing? This could help narrow down if you're dealing with the same issue I had. The M series are amazing cars but they can be a bit finicky with their electronics!

Thanks for the detailed response! My car has been perfectly maintained with the last service done at 15299 KM, and this issue just started showing up last week. The check engine light is steady, and yeah, the vibration definitely gets worse when I rev it up. Using my 's scanner, I'm getting a P0301 error code. The weird thing is, the vibration seems more noticeable in the morning when it's cold, but it's still there even after the engine warms up. I'll definitely look into the ignition coils, that seems way less scary than an engine mount issue. Just hoping it's something simple like what you experienced.

Hey again! Yeah, that P0301 code confirms my suspicions, it's exactly what I had with my M4. It's actually really common in these engines. That code specifically points to a cylinder 1 misfire, which totally explains why you're feeling those vibrations, especially during cold starts. Given what you're describing, I'm even more convinced it's similar to what I dealt with. The cold morning symptoms are particularly telling, that's exactly how mine acted up. The loose connector on my ignition coil would contract in the cold, making the connection even worse until things warmed up. Since your car's only got 15299 KM on it, I'd be surprised if it was anything major. These M engines are pretty solid when properly maintained, which sounds like you've done. My advice would be to head to a shop and have them check cylinder 1's ignition coil and connector first. Might save you a bunch of money compared to messing with engine mounts. Just a heads up, when I got mine fixed, they ended up checking all the coils and found another one that was starting to show signs of wear. Might be worth having them look at all of them while they're in there. Better safe than sorry with these performance engines, right? Let me know how it goes, genuinely curious if it turns out to be the same issue I had!

Thanks so much for the follow-up! That's actually really reassuring to hear that your issue was so similar. The fact that yours also acted up more in cold weather makes me feel a lot better about this whole situation. I was really stressing about potential engine mount repairs and the costs involved. I've scheduled an appointment with my mechanic for tomorrow, definitely going to have them check all the ignition coils and connectors like you suggested. You're absolutely right about being thorough with these engines. I'll make sure they inspect everything while they're at it. Really appreciate you taking the time to share your experience in such detail. It's helped me understand what I might be dealing with, and honestly, it's such a relief knowing it could be something relatively straightforward to fix. I'll update you once I get the diagnosis, fingers crossed it's just those coils!