tomeads:

Reading voltage at the throttle switch is misleading; the switch grounds either the idle controller (ICU) at closed throttle (Pin 1), or the ignition controller (EZL) at WOT (Pin 3). Pin 2 is the ground.

Your test should be to look for continuity to ground from Pin 4 of the ICU socket with the throttle closed. (Remove ICU from socket)

Since you did not mention idle speed in RPMs, what is your view of "fast"?
And, does the idle speed change between Neutral and Drive?