I wanted to share some info on my successful fix for code PO121, indicating problems with the throttle position sensor. I followed Youtube instructions on removing, cleaning and replacing the throttle body. I was able to find just the sensor, part number 19-259-452. It was $43 delivered. Most posts say to clean throttle body and replace the whole thing if cleaning does not work. Replacing the sensor just involves removing the 6 metal clips that hold the black plastic sensor to the throttle body. It pops right off. Discard grey gasket...new part comes with new one installed. Boston Volvo sells the part online.