Idle air controllers are widely used in auto fuel injection systems to control volume of air supply, making motor speed reach a demand objection. It is incorporated a permanent magnetic rotor, magnetically conductive stator and thread shaft which turn rotary motion into line motion. It uses step signal supplied by system to control switch, so that the rotor run in clockwise or anticlockwise, making the thread shaft pull in or pull out, accordingly the cross section of the air passage is adjusted, further it stabilizes the idle speed and reaches an ideal speed.