The fast idle adjustment is preset by the engine manufacturer to comply with emissions requirements and is not adjustable. Tampering with the fast idle adjustment may result in fines or penalties.
If it is determined that either the fuel injection pump or governor assembly need repair, they must be replaced only as complete assemblies. Only an authorized factory trained technician is allowed to remove and install these assemblies. If replacement is necessary, remove and install the fuel injection pump or governor assembly as complete, individual assemblies.
Because the fast idle is not adjustable, the throttle cable adjustment becomes critical to proper engine operation. Therefore, first make sure that the throttle cable obtains its full range of motion, stop-to-stop, before performing any diagnostic procedure.
 – Place a small piece of tape on the flywheel
 – Start engine and run for 5 minutes to obtain normal operating temperature.
 – Move throttle lever to fast idle position.
 – Use digital tachometer to measure engine speed at flywheel.
– If engine speed does not meet specification carefully check throttle cable adjustment.
– If engine speed still does not meet specification, have governor inspected by an EPA authorized diesel service (ADS) center.