Hmm, I haven't heard about this on the N20, HPFP? (Just kidding, I hope, that issue was suppose to be a thing of the past with a newer part design)
It's been a couple a month or so since I dug hard into researching the N20 and current problems reported (Didn't ever see anything like this reported anywhere) but doing some reading up on the other model forums that also use the N20 wouldn't be a bad idea to see if anyone has posted the same issues there in the last month.
I don't understand the fuel trim though. Where were you driving? Any place abnormal for temperature or elevation? My wife had an A3 that always had the turbo shutting down randomly when we drove in Phoenix in the summer -- Great dealership there, offered to bring in a tech and solve it on a Saturday at 6:00PM but said it would go away 50 miles outside, it did, and only returned when were in that area.