While I may not have as many years as some tech's here
I have spent a LOT of time with the 1980 vintage engine
and its arcane control systems.

The high idle speed is the norm until the engine is HOT. Both my
1980 SL and SEL will reach 1800 rmp before beginning a gradual
slow down to 650 rpm.

I spent weeks trying to understand how the major and minor devices interrelate because I was convinced that no-one would design what is essentially a "Choke System" and would make it so complicated and do it deliberately.

From my memory, here is an overview:
There are at least three major units involved.
Warm up compensator, idle speed air controller, and a distributor
with a vacumn controlled retard. When the engine is
cold the warm up compensator changes the differential pressure in
the fuel distributor using a heated bi metal element acting on the
bellows within the unit. As the operating temp is reached the strip
normalizes the external pressure on the bellows which then normalizes
the fuel distributor pressure and leans out the mixture.
The idle speed air controller also works on a temp controlled air
flow allowing more air to flow if the engine is cold.
The vacumn controlled distributor will retard the spark until about
50-60 degrees c is reached so about the time you would expect the engine to slow down the spark is "advanced" (removed from the retard position)
and the engine speed leaps forward again.

I am writting this from work and possibly could add some details
when I get home and get my paper manuals and notes if anyone
is interested.