M-DCT Lag - What's the reason?

[nitramsen]

It's been a 15 years since this chat—how time flies. Haven't had an M3 E90 since 2012 after BMW had to take mine back because of that gearbox mess. Fast forward, and here I am, picking up a Z4 from November 2009 35i DCT,with engine damage (spun bearing, these N54 and oil supply). Got the engine fixed up and all the software/firmware updated to the latest versions, and I gotta say, it felt like they finally sorted out the DCT issues that bugged my old 2008 M3—or so I thought. The car was smoother with barely any lag after hitting 400km.

But then, around 500km, that old, annoying lag started creeping in at roundabouts and in stop-and-go traffic. Totally not fun. Things went south at 850km when the car just stalled and wouldn’t kick back to life. Turned out, it was all because of a loose ground wire to the DME (Stupid me, loose nut holding the ground wire). Fixed that, and boom, the lag vanished like it never existed. Makes me wonder if some of the DCT drama from back in the day was just bad wiring. Anyway if your DCT's acting up and you can't figure out why, might be a good idea to check those ground wires (There were many error codes stored, from the fuel pump to ABS, related to the ground wire issue, not just the DCT. However, there were zero codes 2 days before it went completely out, and the ground connection must have been dangling long before that).