How tight should the throttle cable be at idle?
The cable must be tightened so that it is taut with the engine at idle without lifting the throttle lever off its idle position. If slack is left, the first part of the potentiometer travel is wasted and the speed starts late; if it is over-tightened, the idle speed rises and the lever can never return fully to idle. The first step in GS740-3P calibration is exactly this taut adjustment.
The definition of the correct adjustment is clear: no slack, no preload either. With the engine at idle the cable will stay taut, but it will not lift the throttle lever off its idle stop.
How it is done:
- Run the engine at idle and set the potentiometer to its lowest position.
- With the servo at the idle position, attach the cable to the throttle lever and tighten it so that no slack remains.
- Verify by ear, and from the speed gauge if there is one, that the idle speed has not risen. If it has risen, the cable is too tight; slacken it a notch.
- Increase the potentiometer slowly and check that the speed responds without delay.
Symptoms: if nothing happens when you turn the potentiometer a certain amount, there is slack in the cable. If the engine sits higher than it should at idle, the cable is too tight. If the lever does not return fully to idle when released, either the cable is too tight or the return spring is weak.
Over time the cable beds in and stretches somewhat; check the tension again after the first hours of operation. On the GS740-3P, if the cable has slipped or been replaced, the upper limit calibration must be redone.
Full topic: Electronic speed and throttle control on a diesel engine