I get a different speed every time at the same potentiometer position, why?
This is called hysteresis and its source is usually friction in the cable run. On a bowden cable with sharp bends or pulled across an angle, the same actuator angle produces a different throttle butterfly position in the upward and downward directions. A slipping clamp, an unsecured sheath and the difference between a hot and cold engine give the same symptom.
Checklist:
- Routing: run the cable by the shortest possible path with the gentlest bends. A sharp turn increases friction and therefore hysteresis. Use the cable guides supplied with the set.
- Sheath: a sheath not fixed at both ends moves a little at every change of direction, and that is deadband outright.
- Clamp: a loose connection slips gradually; the speed drifts downwards over time.
- Engine temperature: on a cold engine the idle and combustion behaviour is different; it is normal to see a different speed at the same throttle position. Make the comparison on a warmed-up engine.
- Signal noise: keep the potentiometer cable away from the ignition and charging cables; if you are using shielded cable, on the GS740-3P connect the shield to the green (pot GND) lead.
Note: the GS740-3P holds actuator position in a closed loop with the AS5600, so the angle is repeatable. What is not repeatable is the mechanical transmission between the cable and the butterfly; that is where the solution should be sought.
Full topic: Electronic speed and throttle control on diesel engines