Thank You, Randall!
I love carbs, too. I think You know because I made pass Your twin IDF setup the German legislation. I could stop tinkering now, they run great! But I can't, so EFI is the next step on the ladder to nirwana
To answer the questions: In the diagram there are two idle valves, but You need only one. They want to show how to wire up the different types of idle valves (2-wire/3-wire).
The purpose is to have stable idle under various conditions.
In most stock EFI systems the throttle is completely closed when the accelerator is released. All the air required for idle goes through a bypass. In this bypass there is an electromagnetic valve to control the amount of air going through. When the engine is cold, it opens for longer periods (or even permanently), when the engine is hot, the open intervals are shorter (pulsewidth-modulation). This makes increased idle speed during warm-up, and normal idle when hot.
Another option is to set the throttle gap to a good idle speed when the engine is hot. The valve is permanently closed then. During warm-up, the idle valve gives additional "false" air through the bypass - fast idle!
Generally we can say: The controller (Megasquirt) is always checking the idle rpm, correcting it when it is too high or too low, with the help of the idle valve.
A third option is a stepper motor which acts on the throttle plate, opening or closing it.
Then no idle valve is required any more, but only Megasquirt 3 can drive such a stepper motor.
My concerns are that the "false air" going through the bypasses in my setup is not enough to let the engine fast idle after startup. So I will probably set the throttles to a certain gap, but this requires syncing, what I actually wanted to avoid.
CHEERS
Ray
