PURPOSE: To cut the warming-up time required for a heating apparatus as short as possible without producing what we call a creep phenomenon, by setting a proper range of idle-up revolving speed in accordance with engine cooling water temperature and automatic transmission gear-shift during operation of the heating apparatus.

CONSTITUTION: A control unit 50 is connected with an engine speed sensor 29 installed on a distributor 27, a water temperature sensor 59 installed on a cylinder block, an air flow meter 15 and an intake-air temperature sensor 58, through which a fuel-injection valve 20 is controlled. In addition, this control unit 50, at an idle, adjusts the opening of a flow control valve 31 installed in a throttle bypass passage 30 and controls it to meet the desired idle revolving speed; accordig to signal from a a heater mode sensor 60 which indicates 'under heating,' a heater capacity sensor 61 which indicates 'top heating' and a shift range sensor 62 indicating 'gear-shift,' optimum desired idle revolving speed is set up in accordance with cooling water temperature and transmission gear- shift.