Although others have claimed otherwise, it seems fairly obvious that the
AFM alone won't accomplish much, and my initial tests indicated that the
engine ran *very* lean if the AFM was the only variable changed (oxygen
sensor disconnected).
What exactly were you hoping to test? If you disconnected the O2
sensor, the ECU would use default open-loop fuel maps. If the BWM AFM
allowed more air flow compared to stock, the fuel map would certainly be
too lean. If anything you just proved that the BMW AFM does flow more
air. With the O2 sensor connected the ecu would compensate for the
additional air with additional fuel... presumably resulting in more power.