I'm not an expert on 850's, 240's being my Volvo experience (I'm really just lurking here to learn about 850's, in case someday there aren't any more good 240's and I have to go to a FWD -- no offense meant, it's just a matter of personal choice :-).

But if you don't get any response, here's what we do for the 240's IAC.

There are three electrical contacts, all in a row. First, use a digital VOM to test the motor for it's circuitry, by testing for resistance: between the center contact and first one and then the other end contacts, there should be about 10 ohms resistance.

If both circuits are good, then apply 12v between the center contact and each of the side contacts -- the little door inside should swing one way or the other.

If it works both ways, then we could probably assume that the IAC is good, and look for another reason. In our 240's, an alternative could be a dirty throttle body -- if you don't use synthetic oil, the throttle body can get pretty dirty in a mere 10 or 20,000 miles.