Been there, done that. I even tried to test the wheel sensors using a write up I found for an E46 (I think). It wasn't good for Z3s, but I did get similar reading on all 4 wheels, so I thought the wheel sensors were most likely OK. I couldn't find any way to check the steering angel sensor or to recalibrate it, so no choice but to go to the dealer.
At least I got to sit in a 1 series. It looked nice. I'll bet they go fast once they get some in they can actually sell (they said this one was demo only and they can't sell any until after the announcement in about a week).