Is there an unused black 3 prong connector exiting the harness along with the gray 3 prong idle control valve connector and the black 3 prong throttle position sensor connector? They all have the same indexing configuration.

The mystery black 3 prong connector has the fixed square "C" retainer clip similar to those used on the fuel injector connectors. The other two connectors have the "slide to release" retainer clips.

I labeled all the connectors I unplugged and I would remember using a pick to get than tight "C" retainer off. Can't see anything nearby that mates and the electronics diagram shows no other 3 prong devices nearby.

It is an extra connector, don't worry about it.