Pulse-Width-Modulated idle control is a system that allows air to bypass the throttle by varying amounts based on the Duty Cycle of a signal sent to a solenoid valve.



It can be thought of as a tap - if the signal is "never" on, then the valve is closed, if it is "always" on, then the maximum air the valve can flow will flow. If we turn the signal on and off rapidly, (usually around 100 - 300Hz) and vary the on time to off time, then the valves flow will also vary by the same amount.



The turning on and off, electrically speaking, is done by the valve usually receiving an ignition switched 12v supply on one pin (or one side of the coil inside), and the ECU turning on and off the ground signal to the other pin (other end of the coil winding), using one of its PWM Low Side Outputs. This makes the plunger inside move forward and backwards very quickly, giving the desired air flow through the valve. Note that PWM Boost Control works in a very similar way only changing the flow to the turbo actuator.


In order to use the PWM (Pulse-Width Modulated) Idle valve, the ME ECU needs to know the valves control frequency (PWM Base Freq), min and max duties, and whether more duty equates to more or less air flow (These should all be available in the valves data-sheet, or from online knowledge bases). Enter these numbers into the relevant fields into the idle driver.


In all cases the PWM valve duty (the percentage of time for which it is ‘on’) will not be modified unless the TPS and RPM settings fall into the desired ranges, which we call the ‘idle zone’. The Idle Status DRO indicates the state of the idle algorithm.