It has to be intake problem. I do get that RPM unstability problem(not as bad though, just slight RPM fluctuation) during cold start, but it goes away quick. Never had such bad problem like you BMWxtreme. Sorry to hear that.
and My simota intake never threw code on me.
Little tip, during install, make sure everything is AIR SEAL TIGHT. Every step should be taken very carefully making sure that everything is perfectly in place. second, when you start the car(cold start), let the car sit for a min or two before you reverse out.