It is not adjustable, and is sealed from the factory and is not to be fulled with. You have another problem that is making you think idle needs adjusted.
Turn the Idle Adjusting screw.
on top of the upper intake there is a screw. it can be used to adjust idle speed.
Computer controlled? Not adjustable
There should be an idle screw right by or under your throttle
Adjust your timing
All Ford vehicles cannot adjust idle nor timing wich is pre-set at the factory and the computer sets the idle and timing, vehicles after 1990 no longer can be adjusted.
May be computer controlled and not adjustable
It could be the Idle Air Control (Idle speed control) valve. Its located on the left side of your TBI and has an electrical connection.
To adjust the engine idle on a 1990 Mazda Miata with a 1.6 engine, locate the idle adjustment screw on the throttle body. Start the engine and allow it to reach normal operating temperature. Then, use a screwdriver to turn the idle adjustment screw clockwise to increase the idle speed or counterclockwise to decrease it, aiming for an idle speed of around 850 RPM. Always double-check the idle speed with a tachometer after making adjustments.
You adjust idle with idle timing
Adjust idle on Mitsubishi diamante
The computer does it for you through the IAC valve Idle air control its under throttle body intake hose.