PURPOSE: To prevent the large increase of the engine speed from the idle engine speed by forbidding the control of increasing the auxiliary air quantity against the deceleration state at the time of a throttle valve being closed when the engine parameter proportional to the engine load is lower than the specified value in the open state of the throttle valve.

CONSTITUTION: An electronic air control unit 25 is formed of a microcomputer 30 for performing the processing of various input data, an A/D converter 31 for converting analog input signals into digital signals to be inputted into the microcomputer 30, and a driving circuit 32 for amplifying duty driving signals to be supplied to a solenoid control valve 16. The angle pulse from a crank angle sensor 22 is inputted into the microcomputer 30 to calculate the rotating speed from its cycle. The analog detecting signal from a throttle opening sensor 24 is converted into the digital signal of the throttle opening value θ at the A/C converter 31 and read into the microcomputer 30. The on-off signal of an idle switch 23 is inputted, as it is, into the microcomputer 30.