All of a sudden my 2002 4.3GXi Volvo is failing under power. The only thing that has occurred from the week previous was that the leg was serviced can this be the cause of the problem or is it possible that something has gone screwy with the EFI as it seems as though it simply runs out of gas. I also noticed that when I pull the revs back the actual engine seems to recover and revs increase even though the throttle lever has been pulled back?