System for controlling idle speed of an engine

摘要

An engine has a bypass around a throttle valve and a solenoid operated idle speed control valve provided in the bypass. The control valve is driven by driving pulses duty ratio of which is dependent on a coolant temperature and an old learning correction value. Temperature of a solenoid of the control valve is converted to voltage. A map is provided for storing normal temperature duty ratios, one of which is derived from the map in dependence on duty ratio of the driving pulses and the voltage. Difference between the duty ratio of the driving pulses and the derived normal temperature duty ratio is stored in a memory. When an ignition switch is turned off, the difference is added to the old learning correction value to produce a new learning correction value. The new learning correction value is used for a subsequent engine operation instead of the old learning correction value.