Engine idling rotational speed control device

摘要

A stepping motor is driven such that a rotational speed of an engine falls within a range of a target rotational speed determined in accordance with at least an engine coolant temperature when a throttle valve is substantially fully closed, in order to control an opening area of an air flow rate control valve. In the control operation, a lower limit of the opening area of the control valve is set to prevent the opening area from being reduced beyond a predetermined area in order to prevent engine stall. A predetermined setting is stored in a predetermined area each time when a vehicle speed signal from a vehicle speed sensor is received and the predetermined setting is decremented under a predetermined condition. When the decremented setting reaches zero, a current lower limit is maintained.