Idle Air Control tech - electronics gurus

In regards to the IAC stepper motor...

- What type of stepper winding does it use? (unipolar / bipolar / etc)
- Anyone know the number of "steps" it uses over its range? Like, to go from idle to say, 2000 RPM?
- Is there any kind of positive feedback to the ECU about its position, or does it just know limits and increments it from there?

Basically what I'm looking for is a way to implement a "hand throttle" of sorts without running a cable from the throttle arm into the cab. Something that I can flip a switch and have the revs go up to around 2000 or so. I've worked with stepper drivers before, and Basic stamps etc so that's not a big deal, just gotta find out what I'm working with here.

(before anyone mentions it, it's a '94 XJ w/5-speed ECU, so the extended-idle function is non-existant, and that wouldn't bump it up high enough for what I want anyway).

Another option that was proposed was to modify the TPS signal - I'm not sure what this does to the ECU though. I know it uses that reading as a factor in the amount of fuel being delivered, so if I were to make it think I was at 25% throttle, I don't know what the result would be. I'm guessing it would probably run rich briefly until it figured out that something wasn't right, then scale it back to try and compensate?

Nothin?

as far as I know it's a PCM signal that drives the stepper motor. So you can't just put 12V to it and it moves. You'll have to figure out the PCM signal and then replicate it, there's a dealer tool that excersises the stepper motor, that would be a great thing to put on an o-spoce and see how the signal modulation works.
I like the idea, and it's interesting, perhaps instead of messing with the IAC you could implement another controlled vacuum leak using a regular servo motor.

Actually I am werkin on sumtin like that -it involves a power window switch-cause when the IAC motor extends an retracts it reversez the polarity- just like a power window motor-I can see the wiring on a diagram I just havent figured out the wiring for the signals yet when i get the time to Iwill post it here.:confused1

Something like this?

http://home.cogeco.ca/~rpaisley4/Stepper.html

It would be nice to have some sort of manual control over the motor. I seem to have a short somewhere or something and my IAC stays wide open, causing the motor to idle at 3K or so RPM. I modified the IAC housing and made a manually adjustible version so I could wheel last weekend but an electric setup would be nice.

markaboo929 said:

Actually I am werkin on sumtin like that -it involves a power window switch-cause when the IAC motor extends an retracts it reversez the polarity- just like a power window motor-I can see the wiring on a diagram I just havent figured out the wiring for the signals yet when i get the time to Iwill post it here.:confused1

Click to expand...

Its not that simple. To turn a stepper motor your need to generate a series of pulses on the windings. The pulses are 90 degrees out of phase with various amounts of overlap. If the phase is leading it turns one way, if the phase is lagging, the motor turns the other way. One pulse moves the motor a given angle. Many steppers require 200 pulses to complete one revolution. By changing the sequence of the pulses and the overlap, you can actually increase the steps required to 400 pulses. I say this to let you know that driving a stepper is absolutely nothing like driving a DC motor. I build stepper drivers for large CNC machines.

look at a wiring diagram it is a dc motor
I understand it is pulse width modulated- but with 12 volts as a supply -internal to pcm-and operate around 5 volts or so.I am going to use my ocsilliscope at werk to see the pulse waveform and voltage it is operating at.The one we have can measure time as 1/10 th of a millisecond and quicker than that like i think 20 uS or ? so I will be able to see it.have you seen a unit that does that like the one here ----> http://www.offroadengineering.com/200%20series.htm. is pricey though. But it probably can be copied cheaply.I just need to figure it out.

It is a bipolar stepper motor and uses an H-bridge control circuit on each of the two windings. The choice of a bipolar stepper allows reduced size and weight for the torque it can produce. There is no positive feedback loop. It uses engine speed and O2 sensing as feedback to adjust the idle air.

My 87 2.5 uses a controlled vacuum leak through a solenoid valve to effect an idle speed increase when the A/C compressor engages. My 88 4.0 uses signals to the ECU to control the idle speed for the A/C.

markaboo929 said:

look at a wiring diagram it is a dc motor
I understand it is pulse width modulated- but with 12 volts as a supply -internal to pcm-and operate around 5 volts or so.

Click to expand...

It is definitely a DC motor, which does not rule out stepper configuration. All wiring diagrams I've seen, factory and otherwise, refer to it specifically as the IAC (or AIS) stepper motor. Pulse width modulation would refer to speed control on a DC motor (this is used in Curtis motor controllers for golf carts and wheelchairs etc) however a continuous pulse, at whatever duty/frequency to the IAC wouldn't accomplish what the actuator is trying to do.

There are 4 leads going to it. A PCM controlled motor still only requires two.

rpyne said:

It is a bipolar stepper motor and uses an H-bridge control circuit on each of the two windings. The choice of a bipolar stepper allows reduced size and weight for the torque it can produce. There is no positive feedback loop. It uses engine speed and O2 sensing as feedback to adjust the idle air.

Click to expand...

This is what I was looking for - and this makes it pretty easy to adapt a control onto using just a simple stepper driver IC. So basically, if I were to have a mode where I would take manual control over it, I could operate it with a controller, and then when I flipped it back, the computer would just scale it back until it was right again. Cool.

I still want to try the TPS, as a potentiometer on that would be MUCH simpler, or a simple resistor would be even more so (I'm just looking for an on/off at this point), so I'll probably fug with that first.