an auxiliary air amount control device for an internal - combustion engine , which for the purpose of permitting uninterrupted control of the number of revolutions of the engine mainly during an idling operation of the engine , enables an auxiliary air amount control valve disposed in a bypass interconnecting the upstream and downstream sides of a throttle valve to be so controlled that the idling operation will be carried out properly even when an arithmetic device serving to set the opening degree or the position of the control valve is out of order . this is effected by feeding a prescribed command value to an air control valve of the solenoid type when the arithmetic device is out of order , and by varying the resistance of the valve solenoid coil as a function of engine temperature , so that the opening degree of the valve is jointly responsive to the fixed command and the engine temperature .