how much to replace eletronic throtle module?

Are there troubled codes stored indicating this is the problem? Is the Check Engine Light on? Has the problem been properly diagnosed, a professional grade scan tool will display key engine sensor data such as air flow into the engine ,engine load, throttle position ect..... to determine if the throttle body is bad. See if you get a copy of Volvo Technical Service Bulletin number 25-149-A it regards this problem. The replacement of the part is about 1.5 hours and the part is nearly $600.

I agree with Pat, you'll want to get this diagnosed, there are several possibilities, the throttle module being one of them. Volvo has extended the warranty on them so I advise taking it to your Volvo dealer to have it checked.