What is the working principle of the auxiliary throttle of EFI vehicle?

When the engine is idling, the main throttle valve is closed, only a small amount of air enters the engine combustion chamber through the idle air control valve, and the auxiliary throttle valve will automatically open, increasing the air flow and keeping the engine at a stable idle speed. The auxiliary throttle can also adjust the air-fuel ratio by controlling the opening to ensure the combustion efficiency and emission performance when the engine is idling.