Cable Pretension
It is the light tension left in the cable while the engine is at idle, which takes up the slack but does not open the throttle lever. The GS740-3P calibration procedure requires the cable to the throttle to be tightened taut while the engine is at idle. With a slack cable the first part of the command is wasted; with an over-tensioned cable the idle speed rises.
Pretension makes sure that actuator movement is transferred to the throttle lever from its very first millimetre. If the cable is left slack the actuator first takes up that slack; over the first quarter of the potentiometer no speed change is seen at all, then the speed rises abruptly. This makes the control behave like a deadband and leaves the user with the impression that the system responds late.
The opposite extreme is more dangerous. If the cable pulls the lever a little even at idle, the engine cannot come down to its true idle, the no-load speed stays high and problems may appear when shutting down. The adjustment window lies between these two errors: when you press the lever to idle by hand a slight tension should be felt in the cable, yet the lever must stay in place when it is released.
Tension is a precondition for calibration. On the GS740-3P the cable must be taut before the upper limit is taught; teaching performed with a slack cable becomes invalid once the cable is later taken up.
Context in which this term is used: Electronic speed and throttle control on a diesel engine