I'm considering designing a controller board for the IAC valve on my 2200 manual because the ECU apparently enjoys pissing away fuel for no reason. These are a few of its bad habits:

1. Idles at 900 RPM warm while my auto runs at a much more conservative 580 rpm.
2. While the car is in motion and in neutral, it idles at 1200-1400 rpm.
3. Between gears, RPMs sometimes shoot up as far as 3000.

Basically, I've pinpointed the ECU's use of the IAC valve as responsible for poor fuel economy. My 1998 auto gets better MPG numbers than my manual, so something is not right. My driving style is good, I keep a light touch on the pedal and stay between 1000-2000 rpm 99% of the time, I don't use the A/C and my tires are 44psi all the way around on stock rims.

I've disabled the IAC valve in a semi-closed position to lower the idle by doing the following:

1. Pulled off the brake booster hose and put my thumb over 90% of the opening, creating a vacuum leak.
2. Allowed the IAC to compensate by closing more.
3. Unplugged the IAC, freezing it in that position.
4. Attached the hose back on to the brake booster.

Observations:

1. Idle fluctuates between 500 and 700 rpm.
2. MPG improves by 3-6 points.
3. ECU doesn't seem to care that IAC valve is unplugged, CEL does not light.

I'm fairly confident that I can design a circuit to keep the idle/cruise RPMs stable at 550, further increasing MPG figures. I need data from you guys on this valve. What I know so far is that it has four pins, is manufactured by Borg-Warner and costs $80.

Is it a DC motor type valve or a solenoid type valve? The fact that it stays in the closed position makes me think it's a motor valve.
What is the pinout to the valve?
Where can I get a connector for the valve?
What are the electrical parameters (voltages, impedences) for it?

Or can I expect a GM tech to be able and willing to reprogram my ECU to idle and cruise at 550 rpm and save me this trouble?

2002 Cavalier 2200 5spd

it is neither a dc motor or a solenoid, it is a stepper motor. there is infohere that should help you figure out what you want.

wiring diagram for it

solid snake, you do know your auto should get better gas mileage?

It shifts at the most economic point direct by its programming.

44psi on stock tires? good lord, where do you drive. I want to keep away from you when those stockies blow.

the sticker on my 2001 says 30 cold, and like 35 warm.

your runing like 50% over spec.

Aww crap, a stepper So much for an analog circuit. Thanks a lot PoundinFire and Ben for the data. I assume, to crank the motor one way, I'd apply alternating positive pulses to the coils and to crank it backwards, alternating negative pulses?

Can anyone recommend an alternate valve I can use for this purpose by hooking it up to a vacuum line? Do DC motor or solenoid IAC valves exist for other cars?

My tires are not stock and are rated for 44psi max (sidewall, not owner's manual rating), so that's what I run them at. I shift either at or below what my auto shifts at and the EPA numbers are better for the manual than the auto.

Also, several shops in the area (including GM service departments) were unable to modify the programming on my car to lower the idle.

2002 Cavalier 2200 5spd

I decided an Atmel 4433 would be a good microcontroller for the job. Anyone know what kind of voltage this motor runs on?

2002 Cavalier 2200 5spd

I still think your tire pressure is wrong.

Maybe someone else can slap me, but as long as you are using stock sized tires. you should use stock pressure.

just because the TIRE says its max is 44psi, does not mean, you should run it at max pressure.

I can't edit my post but heres a good link.

http://www.cartalk.com/content/columns/Archive/2006/January/01.html

So I think until you learn how to correctly set your tire pressure you should back away from you IAC before you screw things up more.

Just like the article says, MFG recommended tire pressure is a compromise between handling, comfort and fuel economy. Handling at 30psi is poor and the tires squeak often. The autocross guys almost always inflate their tires beyond what the car manufacturer recommends to keep the sidewall from collapsing. I don't drive my car nearly as hard as they do. The roads around here are paved more or less perfectly and there are no potholes to avoid. I'm within the tire manufacturer's spec for safe operation and I recognize I'm trading some ride comfort for fuel economy. 42mpg highway doesn't come free. As long as I'm within the tire manufacturer's range for safe operation, it's just a matter of preference, just like oversized rims or ridiculous wings.

2002 Cavalier 2200 5spd