•  The variable tumble system functions to lower emissions at cold-engine start.

•  At cold-engine start, the variable tumble system increases intake airflow speed by closing the shutter valve to narrow the intake passage. As a result, the air-fuel mixture quality from the injector is improved. Additionally, the creation of a powerful air tumble in the combustion chamber promotes the atomization of the air-fuel mixture. Due to this, emission efficiency is improved.

•  For variable tumble control, refer to CONTROL SYSTEM, VARIABLE TUMBLE CONTROL. (See VARIABLE TUMBLE SYSTEM FUNCTION [ZJ, ZY].)