In the early archives there are some descriptions of replacing a burned
out transistor in the Idle Control Unit.  I don't know if your damage is
the same.  I found the described transistor was burned out on my ICU so
I replaced it with a larger current carrying part.  The system
functioned after that but would still give problems with racing idle
occasionally.  I finally decided it was heat causing the occasional
problem because it would fail with the plastic cover on but would work
OK with the cover off.  This failure mode was occasionally racing idle
(~4000 rpm) that got more frequent with age.  I finally cut a hole in
the plastic cover and extended the transistor out the hole and added a
heat sink outside the plastic cover.  I didn't seem to have any problem
with the electronics being exposed to the water and dirt because of the
hole.  That worked for years until I did a Subaru conversion.

I think the Idle Control Valve began to draw more current as it aged
causing more heat in the load carrying transistor in the Idle Control
Unit.

I can dig through my files for my records if anyone is interested.

Ed