Well I have had my X1 (sDrive28i) literally a week and yesterday, driving slowly in a shopping center parking lot, there was a loud BEEP and then a flashing message on the IDrive:
ENGINE MALFUNCTION - ENGINE IS OPERATING ON REDUCED POWER. GO TO YOUR NEAREST BMW CENTER.
We had been shopping, returned to the parked car, drove it a few minutes, nothing at all noticeably wrong, when this happened. We weren't far from home, and what are you going to do on a Saturday at 5pm? I doubt BMW service has emergency hours.
As we continued driving, traffic was fairly heavy, but it did seems as if the engine was working hard. Oh and the icon in the trip computer is an engine half-shaded in.
We had one more small stop on the way home, so I went ahead and parked. And when we came out and started the car, the message did not reappear. However, we were less than 5 minutes from home at that point.
So I will take the X1 out later today and see if on a longer drive, the message reappears. If so, I'll go straight to BMW Beverly Hills service tomorrow morning. If the message doesn't reappear, I'll just call and make an appointment to come in for an evaluation.
I did some searching for "BMW Engine malfunction - reduced power" and got a surprising number of hits, but for other models. Seems to be several possible causes, with fuel line problems frequently mentioned. We'll see...