occurs immediately after an escape from the low load zone z this decision may be made through the decision as to whether or not the previous decision has the low load zone z when the zone z occurs immediately after an escape from the low load zone z the counting operation of the inner timer that is a timer determined by the program which has the predetermined time for example of about two seconds starts at step 13 when it is decided at step 14 that the running count of the timer has not yet reached the timer set time the power mode increment correction factor c pw for example about 0 15 is set at step 11 as in the case of the low load zone z if the z zone does not occur immediately after an escape from the low load zone z the power mode increment is performed when the zone is not the z zone or when the time of the timer in step 13 is within the set time after the set time passes the timer is reset at step 15 to release the power mode increment therefore even when the zone has escaped from the low load zone z the power mode increment continues during the set time from the escaped moment as described hereinabove thus two ranges of low load operation exist a first low load range during which fuel enrichment is subject to a restricted condition e g time limit extends for example to a high rotation high load side of operation this first low load range occurs immediately after a transition out of the low load range z the low load.