A servo motor operated rotary air throttle has a driving member connected to the throttle shaft. The motor rotor is connected to the driving member in a lost motion connection. If the throttle is lodged due to ice formation, the motor rotor acquires rotary momentum relative to the driving member during the lost motion rotation and a projection on the rotor impacts the end of a slot in the driving member to impart a momentum pulse to the driving member and throttle shaft and dislodge the throttle.