PURPOSE: To prevent engine speed from being abruptly increased, applying a correction signal, to an actuator, for controlling the control parameters of engine speed with a predetermined time delay or gradually from the time when a transmission is shifted.

CONSTITUTION: In a computer 13 which controls an actuator 5 for driving a throttle valve 3 in an intake pipe (not shown), through solenoid valves 11, 12, there is provided such an arrangement that voltages Vset, Vrpm corresponding to the targed and actual values of idle speed are delivered to a comparator 22 for calculating a control signal V1, the shift position of a transmission (not shown) is detected by a signal from a shift detector 30, thereby a switch 29 by which a constant voltage Vcon corresponding to a part of engine load is delayed and delivered to an adder 26, is controlled. When the transmission is shifted to its drive position from its neutral position, the switch 29 is turned on so that the delayed voltage Vcon is added to the signal v1 for controlling the valves 11, 12.