Hmmmm… last 20R I worked on was a 77 Celica.

Does it have a water heated choke or an electric one?

I'm trying to remember if it had a vacuum operated high idle pull-off or not. If so, I'd check vacuum lines and switches. If not… jeez, got me.

Was it sitting for a long time by chance, like maybe some of the smaller coolant passages in the intake and such are clogged? I remember the Celica had coolant passages right under the carb to prevent icing in the winter, and it took a solid week of running it (after sitting for 18 years) for the blockages to dissolve and push through.

About the only other thing I can think of is maybe one of the tiny clips fell off and let a small arm come disconnected that would normally kick the fast idle cam down.

Let us know what you find, or maybe snap some pics?

My Truck: 1987 XtraCab DLX 22R 4WD 5 Speed Manual
"Speed has never killed anyone. Suddenly becoming stationary, that's what gets you." -Jeremy Clarkson