I have a 1993 18hp Volvo diesel model 2002 engine.I am trying to figure out how to adjust the idle. Right now it idles at 750 rpm and according to the manual it should be 850rpm.I have the owners manual and the repair manual and neither have instructions on this adjustment.I asked a Volvo dealer but he had no idea how to do it.I can see a set screw with a locking nut on the throttle housing where the throttle cable connects on the engine, but I am not sure if that is it.Can anyone help me?