Z3 2.2 M54 Engine Management Woes !
Yeah, thanks Mikey - that sounds like really good advice. I did get the OBD fault codes read by the same guy who threw in the MAF sensor, but they seemed quite vague (relating to certain cylinders). Although he re-set the diagnostics & suggested that I took her back for a second go, I decided not to because I didn't warm to him, and I didn't want any more dings in my tail through dodgy parking....
But you're dead right. Without a code reader, it seems that you're stumbling in the dark with modern vehicles, so I've got a handheld device on order. Can't wait to give it a try !