Check the pcv system for restriction. For this you need a special gage to be able to read this. If it is plugged up then you will need to clean the the pcv system and remove the throttle to clean it. Also you may not have engine management codes but you could have codes set for the electronic throttle module. Also you may want to call Volvo to see if you still have the 10year/200k mile warranty on the throttle? The warranty expires base on the delivery date of the car. So if it was bought and delivered say Nov. Of 2009 then the warranty has expired already? But Volvo could tell you that for sure.