Weird Engine Issue

[dmytro98]

The car is a 09 128i with the n52 and 66k miles. Has a n54 intake manifold, catless headers and stage fp tune. Spark plugs were replaced but I think it's still on the original coils.

Recently I've been having some weird issues with what I think are misfires along with the engine feeling like stumbling or just cutting out.

Misfires
They are super subtle and mostly happen under partial throttle but very inconsistent. I'll be able to drive the car for a couple of days without any issues, but for others it does it a couple of times. I don't get any codes or anything so I don't really know where to start.

Stumble
This one might not be related to the misfires but another weird problem. When I took the car drifting I noticed that it would almost stumble or cut out when I went to do a clutch kick but it was only ever on my first initiation. I never had it happen in the middle of a lap, always the first initiation. I was thinking fuel slosh maybe but It would do it even with more than half a tank, but was especially on the track with the bank. Luckily I was able to get that one on video. Also very inconsistent as most laps I would have no issues.

Stumble/Engine cutting out
https://youtu.be/ya0D0ScAjOk

Any help would be appreciated.

[foilman]

Sounds more like plugs than coils if it's that intermittent. Are you sure they were gaped correctly?