The throttle switch doesn't have a code for "out of range". It's simply open or shorted. Setting the throttle switch voltage lower does indeed change the injector duration throughout the entire band. Lean isn't necessarily good. Especially with today's fuels. Sometimes it's like flushing two toilets, when you only use one........... I've never been a big fan of trying to cheat the system. If you have 1400-1600 rpm cold and it settles to the correct rpm warm, there's nothing wrong with your aux air regulator. The only way I know to get 3-4 more miles per gallon, rests with your right hand.