Ford ISC-BPA

[Dave Williams]

 How does the Ford idle air valve work?

 From the initial descriptions I found, it was a solenoid, pulsed
rapidly to shuttle the valve open and closed to meter air.  Now I've
found some descriptions that make it sounds like it's fed a pulsewidth
modulated signal that varies the voltage, pulling the solenoid only
partly open as needed to meter air.

 Using it like a shuttle valve would be easier in software; using it pwm
would be harder since you could never know exactly how much air the
valve was passing, since there would be no feedback from the solenoid's
position.