A direct-injection internal combustion engine is fluidly coupled to a passive SCR system including a three-way catalytic converter upstream to an ammonia-selective catalytic reduction catalyst. Transition from an HCCI combustion mode to an SI combustion mode includes determining a preferred air/fuel ratio to achieve a minimum fuel consumption and maintain combustion stability at an acceptable level for a predetermined engine operating point during the SI combustion mode. A fuel injection timing, an engine spark timing and an engine valve lift are substantially immediately controlled from respective HCCI combustion mode settings to respective SI combustion mode settings. A transition to the preferred air/fuel ratio is coordinated with a transition of an engine valve phase from a respective HCCI combustion mode setting to a respective SI combustion mode phase setting.