My 2008 Volvo 5.0gl-J surges or revs up and down at low speed or in idle. the carb was completely rebuilt but same issue. I have a mechanic looking at it but he keeps telling me that the carb might need an adjustment I have tried every possible setting and still can't get my engine to idle at 600 RPM's and stop running rough and stop revving up and down. If i apply more gas its fine and i can run at higher speeds no problem. Only at low speed or idle to i get this.