More pulses means more bandwidth (speed increase).
The IAC valve is mounted on the throttle body to control engine idle when commanded by the engine control unit (ECM). The ECM sends voltage pulses to the IAC valve stepper motor windings to move the valve needle in or out a predetermined distance (step) with every impulse. The movement of the needle controls the valve's air flow, which in turn controls the engine's idle speed. The required idle speed for all operating conditions is set in the ECM calibrations.
Parameters affecting the idle speed control:
- coolant temperature,
- park/neutral switch position,
- car speed,
- battery voltage,
- pressure in the air conditioning system (if it is installed on the car).
ECM «remembers» appropriate IAC valve positions to ensure a stable warm idle speed with various combinations of the above parameters. This data is stored in the ECM ROM. The data is retained even after the ignition is switched off. The rest of the IAC valve positions are calculated from this stored data.
As a result of deviation due to wear and deviation in the minimum position, the throttle valves (within acceptable limits) have no effect on idle speed. This also means that if the power to the ECM is turned off while in parking mode, (battery removal) Possible idle control failure. This will require further depressing the accelerator pedal during engine start until the ECM locks the idle speed.
The minimum throttle position is set at the factory with the top screw. This setting allows enough air to pass through the throttle valve, which causes the throttle valve needle to move the required number of steps from its seat, to «given» Idling. The minimum throttle valve position on the engine should not be considered the minimum idle speed setting as it is on other types of fuel injected engines. The top throttle screw is capped at the factory after adjustment.