Idle Air Circuit

I am putting fuel injection in a Austin-Healey, and making my own Idle Air Motor housing. I need to know if, with no power present, it the idle air circuit is closed (no air), or open.

healeyplayer

Welcome!

This sounds like an interesting project worthy of a separate thread.

If you are using a stepper motor type idle air motor then it will remain at the position last commanded by the ecm. In most systems I've worked with the IAC is opened up considerably when the engine is shut down.

My problem is, I have a new Stepper motor, and need to know the dimensions needed to make the housing. I don't know if the stepper is extended or retracted at this point, and whether I want to make the adapter sealed to begin with, or open to air passage.

There's probably no standard for shipping stepper motors. They can arrive extended, retracted, or anywhere in between. Many are fully retracted in my experience but not all. What is the original application for the motor? Maybe someone here can measure a throttle body and get some dimensions?

I believe it was for a '88 -'89 GM throttle body using GM#5235277 injectors, which I am using for my installation in custom adapters on SU carbs.

You'd be better off having a TBI in hand to work with and measure.

For an external IAC take a look at this post for parts needed and building one. Easiest way I have found to use GM IAC in an application like yours...

http://www.gearhead-efi.com/Fuel-Inj...ll=1#post38148

At one point I had measured all the dimensions of the IAC passage in a throttle body, and modeled it SolidWorks as part of a custom throttle body that would bolt to a standard Holley base plate. Yes Mark is right, it should not be too hard to get a junk TB and a set of $10 Harbor Freight calipers and measure all pertinent dimensions.