It seems to be happening once a week, sometimes more often, but atleast every Saturday I've had it for the last month or so.
I don't know about the monitoring device, at least that they can leave hooked up. I know they have one that reads the codes, but they haven't offered to leave it hooked up.
It's been in the shop for the 5th time now.
I've been keeping a record of the whole thing at
The Optima Problem. If you're interested, check it out for lots more detail.