leads 78 and 72 accordingly the rod 28 is retracted to the position c thereafter by the signal of the contact switch 64 the rod retracting circuit 71 operates to retract slowly the rod 28 to the position d as described above mode 9 and fig7 show such a throttle opener effect the throttle opener effects to prevent the misfire of the engine the misfire occurs in the negative torque condition of the engine such a condition as the throttle valve is closed on the descent fig5 shows the range in which the misfire will occur since the throttle opener keeps the throttle valve in an open condition for a predetermined time at the deceleration the misfire may be prevented now hereinafter describing the operation for the air conditioner an air conditioner 80 is operated by closing an air conditioner switch 81 by closing the switch 81 semiconductor switches 82 83 and 84 are closed so that each set value of comparators 51 58 and a d converter 52 is raised therefore the motor 41 is operated to project the rod 28 so as to increase the idling speed to the raised level when the switch 81 is opened the rod 28 is retracted to the position d modes 10 and 11 show such an operation when the ignition switch 46 is opened a run on preventing circuit 85.