IAC motor

[steve ravet]

> Date: Tue, 19 Oct 1999 07:53:07 PDT
> From: "Gary Moulton" <gmoabrim at hotmail.com>
> Subject: Manual control of IAC motor
> 
> Can someone tell me which terminals of the IAC motor runs the pintle in and
> out? The wiring diagrams show two coils and the connector has 4 terminals.
> Does one coil send the position back to the ecm and the other is a 12 volt
> reversable dc motor?
> 
> Application is 1994 Mopar 4.0L EFI in a 1982 Jeep CJ-7, and what I want to
> do is be able to manually adjust the idle lower than the 750-800 rpm when
> off-roading. I have connectors and a harness and some electrical experience.
> I plan to have a switch to disconnect the IAC from the system for manual
> control and a spring loaded switch to "bump" the IAC position in or out.
> There is a company offering such a controller for more money than I think it
> should cost to build one myself. Thanks in advance
> 
> Gary M
> gmoabrim at lasal.net

Gary, the IAC is a stepper motor.  There's a very good explanation of
steppers on the internet right here: 
http://www.cs.uiowa.edu/~jones/step/

A stepper motor has two coils in it, and the ends of both coils are
brought out to the harness resulting in 4 wires.  If you energize one
coil the rotor will rotate to a position aligned with that coil.  If you
energize the second coil the rotor will rotate a little bit to be
aligned between the two coils.  If you turn off the first coil the rotor
will rotate a little more to line up directly with the second coil.  If
you energise the first coil again with the opposite polarity of the
first time the rotor will rotate a little more, and so on.

Basically the ECM applies pulses in a particular sequence to the four
wires to produce rotation, where each pulse results in some amount of
rotation of the motor (a couple degrees or so).  The motor can be made
to spin either direction by changing the polarity of the pulses.

That's a simplified explanation, if you want more details the link above
has everything you could want and then some.

--steve

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com