Tune don't control the ISCV voltage points. You actually sychronizing the the throttle to the map. I hope I'm not confusing you. If you was a machinist I say your homing the machine and the controller (CNC computer) the ISCV is a parameter like the tool compensation. Everytime you cycle the key the ecu, measure air temp, atmospheric pressure conditions, water temperature then it calculates the offset of the throttle zero. It cycles the throttle stepper motor and monitors the actual movement of the primary throttle shaft via the Primary TPS sensor.