Oh yes, my 940 turbo has a a very slight miss when you switch the airco on, always has had, and I've never been able to figure out why. Last summer it got worse, mainly because the car was due a service so I sent it to the main agent for diagnosis. I described the fault to them and how it could be provoked.

Five in the evening I went to collect the car, and was presented with a bill for 230 Dollars (well the equivalent thereof). So I said "OK, so what was wrong with it"?

They answer was "we've taken your car for an extensive test drive and found that under certain conditions there is a slight miss with the airco switched on". I know, said I, what's causing it? "We don't know, we have to investgate that further".

I was not impressed!