The Haltech idle Speed motor is a 4 wire stepper motor controlled idlevalve, this valve allows the ECU to control the volume of air entering the intake manifold at idle.
The failure of valve opening sensor would cause valve management of DEH system working confusedly, and result in large scale change of turbine power in the case of governing stage pressure loop idle.
This paper describes the idle speed control stepper motor type composition, Stepper Motor Idle Control Valve on the main structure, Idle Speed Control Stepper Motor Control Principle of the device.