I'm having the same problem with new DISA, clean ICV, intact intake boots, 20k miles plugs, < 20k fuel pump and filter, Techron 2k ago and < 1k oil. (I didn't do all of this to fix it lol it's just the state of my car currently)
Starts at 1100, drops to 800, up and down 800<>1100 and stabilizes at 800 after. ICV did a huge difference - it only 'coughs' twice until it stabilizes, while it struggled 6-7 times before. Improved MPG as well. Takes 45 minutes, just do it
Next steps are O2 sensors, which are original (and thus due twice already on my car based on BMW's recommended replacement interval), reverting my ECIS CAI back to a stock airbox with a new filter. I also need a DME upgrade to the latest version. If you want to check your O2's the manufacture date is on the connectors under the engine cover.
Let me know your progress - I'll do this as well.