I know you have local sources, but I have a few ICV and ICR (speed control) units in my garage, if you need 'em.
It must be the Idle Speed Control black box. The thing leaves the ICV wide open. When it is racing, I can unplug the connector with no change, even though when cold, if I unplug it, the engine races, and settles down as soon as the valve is plugged back in.
I did open the ISC. The piggy-back board was all sticky. Maybe overheating, though it never felt hot. I wiggled it around with the cover off which resulted in no difference.