Well it finally happened to me too guys. I got a CEL yesterday after some quite spirited stop start city traffic, I phoned the dealer first thing this morning and they fitted her in this afternoon flashed the ECU and a TSB relating to overboosting was the cause not actual overboost but an error reading overboost. This plus a check on the trans drain back TSB plus a general chat it took about 45 mins to reprog the ECU but I have to say she is smoother and much easier to drive after such a simple fault.
I was being asked about economy and was again told once I get past 5000 miles she will start to lossen up and give better mileage, though in the past week it has been getting steadily better based on the EVIC display.

_________________
06 Cherokee CRD Limited Automatic
97 BMW 750i