Hmmm, I'm tempted to say that one of the modules is faulty (the phone module when disconnected makes the mk4 work ok??) and while the test in in place it takes priority on the ibus (which makes it work).

Thats a guess though.

I'd start by replacing modules till it works reliably.

__________________
Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.