Truck Repair: c8.3 idle low, locknut, valve lash

Question
rv has 73000 on it. recently started idling around 500rpm. dropped from higher idle but dont recall what it was. engine sometimes stops when idling. What is the idle rpm speed and how may I adjust it. Also how can one tell if the valve backlash is bad. Thanks in advance. Bill

Answer
If it is a manual engine there is an adjusting screw that wears the throttle rests on.It takes a 10mm wrench to adjsut it.It has a locknut on the bottom,lossen it & turn screw couterclockwise until it is correct & tighten nut up.Should idle around 750 RPMs.Valve lash on the manual engine is 0.012 int & 0.024 exh.The owners manual tell you hou to adjust valves & intervals.