AIR CONTROL VALVE.

There is no IAC Valve on this car, it has an Electronic Throttle Body or 'drive by wire system' which means that a little computer module sits on the Throttle Body and controls all the acceleration/deceleration. Best to have the ETC ( Electronic Throttle Control) system scanned and diagnosed. They do fail, once in a while. If you Diagnose and determine the fault of the ETC Module or one of the sensors, ( there are 4 ) you need to reprogram the Engine Computer after you install the part, to adapt to the new ETC ( Electronic Throttle Module ). A new Bosch electronic Throttle Body costs $588 and does require the dealer to program it, I just checked my Volvo parts source. This is not going to be sold a general type of parts store. Need to match the part number and VIN code to the new part.

In addition to what dandd said, there's an extended warranty on the ETC system, Volvo extended it to 200,000 miles and 10 years, so check at your local dealer to see if you are still covered.