Abstract: A heater, which comprises an element whose resistance varies with changes in temperature, and a temperature element are provided in the air intake pipe of an engine. This heater and temperature element together with resistors form a bridge circuit to which heating power is supplied via a transistor. An engine control unit generates start signals Tin simultaneously with the rotation of the engine. A flip-flop circuit is set by these start signals and, when set, the transistor is turned on and the heating power rises. The output signal from the bridge circuit is supplied to a comparator and the output signal of the comparator resets the flip-flop circuit, which outputs a pulse-shaped signal representing the airflow quantity as a length of time. This pulse-shaped time signal is sent via a constant current circuit to another comparator, where it is compared with a reference voltage and the output signal from the comparator is supplied together with the above time signal to an exclusive OR circuit.

Abstract: In or idling speed control system for engines, a bypass passage is branched off from a main intake passage located upstream of a throttle valve and is connected to the main intake passage located downstream of the throttle valve. A flow control valve, actuated by a step motor, is arranged in the bypass passage. The step motor is controlled by an electronic control unit so that the engine speed becomes equal to a predetermined speed. When the engine is stopped, the flow control valve opens the bypass passage to the maximum extent so that the engine can be easily started at the time of next engine start.