idle control valve

[john spears]

On most GM engines, the idle control valve, called IAC (idle air control)
actually opens farther as you push on the accellerator. This is called the
"throttle follower" mode. The more you push, the farther it opens. I think
they do it this way so that when you let off the gas instantly, the IAC is
there to "catch" it and bring it down to idle instead of the sudden
transition when the throttle closes. You can watch the IAC counts on a
scanner and see this going on.

                John Spears
Speartech Fuel Injection Systems