An engine rotation speed during idle running is feedback controlled to a target rotation speed. A basic ignition timing is set based on the rotation speed during idle running, and the ignition timing is feedback corrected based on a difference between a target rotation speed and a measured rotation speed. This feedback correction process and other processes including the setting of the basic ignition timing are separated. A high response ignition timing feedback control is performed by advancing the measuring timing of the rotation speed to a point earlier than the correction timing by at least the processing time required to perform the feedback correction process, and preferably by a value near the processing time. A high response fuel injection amount feedback control may also be performed by a similar process.