More pulses means more bandwidth (increase in rotation speed).
The IAC valve is mounted on the throttle body to control engine idle speed as commanded by the engine control module (ECM). The ECM sends voltage pulses to the windings of the IAC valve stepper motor to move the valve needle in or out a specified distance (step) with each pulse. The movement of the needle controls the valve air flow, which in turn controls the engine idle speed. The desired idle speed for all operating conditions is set in the ECM calibrations.
Parameters that affect idle speed adjustment:
- coolant temperature,
- park/Neutral switch position,
- car speed,
- battery voltage,
- air conditioning system pressure (if one is installed on the vehicle).
The ECM "remembers" the appropriate IAC valve positions to maintain stable idle speed when the engine is warm under various combinations of the above parameters. This data is stored in the ECM ROM. The data is retained even after the ignition is turned off. The remaining IAC valve positions are calculated based on this stored data.
As a result of wear and tear and deviation in the minimum position, the throttle valves (within acceptable limits) have no effect on idle speed. This also means that if the ECM is disconnected from power supply in idle mode, (battery removal) idle speed control may fail, which will require additional pressure on the accelerator pedal during engine start-up until the ECM detects idle speed parameters.
The minimum throttle position is set at the factory with the upper screw. This setup allows enough air to pass through the throttle valve, which causes the throttle valve needle to move the required number of steps away from the socket, at a "preset" idle speed. The minimum position of the throttle valve on the engine should not be considered as setting the minimum idle speed, as on other types of fuel-injected engines. The upper throttle screw is capped at the factory after adjustment.