Ok. I think this time around some is going to kill me. But before you do, please clarify the following:

Car: 1999+ Protege ES

There is a screw on the throttle body which allegedly controls the air portion of the air-fuel mixture. Pushing it down reduces the amount of air and thereby reducing the idle rpm

But then there is the ECU which adjusts the idle automatically to 700 rpm.

The question is:
If the air adjust screw is set to have a lower air flow, in essence, creating a rich mixture, the ECU overrides it and adjusts it create an optimum air-fuel mixture by:

1. simply decreasing the amount of fuel
2. Increasing amount of air
3. bring both air & fuel to as-specified standards

 

Number 3. There is NO way to manually control the idle mixture using the stock PCM. Sorry.

 

No need to be sorry.
I am intrigued why the heck did Mazda provide the AAS screw if the computer is goign to override it anyway?

 

I'm not sure. I think it's there in case something goes wrong with the throttle body.

 

 

The AAS screw is there for base idle adjustment . This is the basic mechanical idle of the engine , it is set with a jumper wire in place between "TEN" and "GRD" in the diagnostic connector . This idle is the reference point for the ECU and if it is too low the engine could shut down on deceleration , too high and the engine will idle high and erratic . This base idle shouldn't be confused with the normal engine idle that is controled by the IAC which is ECU controlled.
This AAS only changes the size of the bypass port for the throttle plate in the throttle body by adding restricting the port as the screw is turned in . It has a nil effect once the throttle plate opens.

 

Only on the old Miata's. Your explanation of how it works was correct, but it should NOT BE TAMPERED WITH!

It is set on an engine bench at the factory, and if it's adjusted by the customer, your engine will never run the same.

It gives you no power, no more fuel economy, no lower of an idle, so why **** with it?

 

But I fcuked with it.
Now how do I set it back?

1999-2000 Protege ES.

 

We adjust them for many idle concerns and I believe there was a TSB for ensuring that the idle is correctly adjust during Pre-delivery inspection . When the ten and grd are connected the engine is running in the initial setting . In this setting the IAC will not control idle.

 

My solution to the Idle problem is over here

Solution