Just a real stab in the dark here, but maybe it's not the gas pedal module but the wiring to/from it, close to the module. So replacement of the module temporarily 'fixed' the wiring issue, but not really. Codes would be helpful too.

Was it diagnosed to have a bad sensor? You need to get the codes and put em in this thread if you want more help. Codes preferably pulled using a volvo scanner and not a generic OBD2 reader, even though it's better than nothing.