PURPOSE: To distinguish the type of a using fuel by detecting the width of variation of engine speed at the time of idling.
CONSTITUTION: At the time of the idling operation of an engine 1, a controller 9 calculates an actual width of variation based on an engine speed signal which is fed back from a distributor 18. The actual width of variation is collated with the map of a reference width of variation to judge whether the fuel in present use is high-octane gasoline or regular gasoline. Thereby, when, e.g., high-octane gasoline is in use, an ignition signal and a fuel injection quantity are regulated to be proper values set in a high-octane gasoline map to control ignition timing and air-fuel ratio. Thus, since the types of using fuel can be distinguished in an ordinary using zone of idling operation, etc. in which no knocking occurs, even when the fuel fed to the engine 1 is changed, the control of ignition timing and air-fuel ratio can be favorably carried out at all times.
MATSUO NAOYA
MORIMOTO HIROSHI
