PURPOSE: To optimize an air-fuel ratio at engine start by opening an adjusting valve on an intake secondary passage until a predetermined time during the detection of a start operation at the time of high temperature starting, opening the valve until complete fuel combustion in a second predetermined time and closing the valve until complete fuel combustion after the second predetermined time.
CONSTITUTION: A control circuit 20 is connected with an intake absolute pressure sensor 10, a crank angle sensor 11, a cooling water temperature sensor 12, an intake air temperature sensor 13, and O2 sensor 14 and an ignition switch 7, and controls an air-fuel ratio via a linear type electromagnetic valve 9 on an intake secondary air supply passage 8. When the ignition switch 7 has been turned ON at the time of engine start, the control circuit 20 makes adjustment as to whether the start is at a high temperature or not, on the basis of a cooling water temperature. At the high temperature start, the electromagnetic valve 9 is closed until a first predetermined time (for example, 1sec), and opened until the detection of complete fuel combustion within a secondary predetermined time (for example, 2sec). And when the complete fuel combustion has not been detected after the second predetermined time, the electromagnetic valve 9 is closed until the end of the combustion.
KUBO SATORU
IKURA HIROSHI
