When CVT was equipped with the engine, fuel consumption of the car becomes economical while the throttle valve angle and the gear ratio of CVT were controlled simultaneously. If the engine was operated with a lean air-fuel ratio(A/F), it is also effective for fuel economy and low level emission. Though fuel consumption becomes economical at transient state by Engine-CVT consolidated control, accurate control of transient air fuel ratio(A/F)also becomes important issue under such control. And then, keeping A/F within the window around the stoichiometric A/F ratio is important for treatment of transient exhaust gas. In these case, SI-SO system was used to control the transient A/F. However, through A/F consists from induction air and fuel behavior, MI/MO system is seemed to be suitable for accurate A/F control for transient state. From such point of view, investigation was carried out about transient A/F control for Engine-CVT consolidated control.