BMW i8 Hybrid Rough Idle, Common Causes and Solutions

Hey there! I've got some experience with hybrids and had a similar issue with my BMW i3 (2014). I also own a 3 series, so I'm fairly familiar with BMW's hybrid systems. Your symptoms sound exactly like what I dealt with. In my case, it turned out to be a loose connection in the hybrid system's wiring harness. The vibration was really annoying, especially at idle. Took it to my mechanic who diagnosed it, apparently, one of the main cable connectors had worked itself loose over time. Total repair was 95 Euro, mostly labor costs for tracking down and fixing the connection. Before jumping to engine mounts, might be worth checking the electrical connections first. Could you share: What error codes you're getting? Does it happen more when the engine is cold or warm? Any recent work done on the car? This info would help narrow things down and see if it's similar to what I experienced.

Thanks for the detailed response! I've got 134809 KM on the clock and had my last service about 2 months ago. The error codes are P0300 and P0301, and I'm noticing the vibration is definitely worse when the engine's cold, especially in the morning. It smooths out a bit after warming up, but the rough idle is still there. Haven't had any recent work done besides the regular maintenance service. Your wiring harness issue is interesting, that would be a much better scenario than dealing with engine mounts! Did your mechanic have to remove a lot of components to access the connections? I'm trying to get an idea of what I might be looking at in terms of labor time.

Hey again! Those error codes you mentioned, P0300 and P0301, actually point more toward a misfire issue rather than what I experienced with my wiring harness. My codes were different (system voltage related). In my i8, when I had misfiring issues a while back, it turned out to be the ignition coils that were failing. The symptoms were super similar to what you're describing, worse when cold, smoothing out a bit after warm-up. The timing of your issue (134k km) matches too, as these parts often need replacement around this mileage. I'd actually recommend checking your ignition coils and spark plugs first. When I got mine fixed, the labor wasn't too bad, took about 2 hours total. Much simpler than the wiring harness issue I mentioned before. My mechanic replaced all the coils as preventive maintenance since they tend to fail around the same time. Total cost was around 800 for parts and labor. Have you noticed any hesitation during acceleration or drop in power? That would pretty much confirm the misfire diagnosis. Also, are you getting any fuel economy changes? These were additional symptoms I noticed with my coil issues.

Thanks for breaking that down! Yeah, I am noticing some hesitation during acceleration, especially when I first start driving. The fuel economy has dropped a bit too, getting about 15% less range than usual. You've actually made me feel better about this whole situation. I was really worried it was going to be something major with the hybrid system, but ignition coils sound much more manageable. I'll get it checked out this week and focus on the coils and plugs first. If the repair cost is around 800, that's way better than what I was imagining for engine mount repairs. Really appreciate you sharing your experience, especially since you've dealt with similar issues on your i8. Hopefully this will sort out both the vibration and those error codes. Will probably just get all the coils replaced like you did since I'm already at that mileage point. Better to do them all at once than deal with this again in a few months!