My '88 Accord has had a fast idle problem for a while now, and after reading this post (especially deserthonda's reply at the bottom), I think I have discovered the problem:
https://www.hondaaccordforum.com/m_14744/tm.htm

After starting the engine, the engine speed rises to ~2200 RPM until the engine warms up. Then(most of the time), the idle will drop to ~1300 RPM. Then(on rare occasions) the idle speed will drop to 800 RPM, but the idle is very rough. I think the previous owners took it to a shop, and instead of fixing the fast idle problem, the shop tuned the carb to cover up the rough idle.

Anyhow, I have checked the thermovalve and fast idle unloader circuits for vacuum leaks and all hoses appear to be OK. I found a new choke opener diaphragm, but have yet to put that on.

Does anyone know where to get the fast idle unloader or the thermovalves? I know there is one thermovalve in the front of the engine, just behind the valve cover. Where is the second one?

 

For starters, you may know the thermo valve "A" has three vacuum ports, one inlet from the engine and two outlets going to the Fast Idle Unloader which has tow vacuum ports. Vacuum is ported in three different stages via these two vacuum hoses.

It appears that there is another thermo valve on the carb with a coolant hose going to it on the same side as the Accellerator pump rod. It looks like that from this pic but I am not 100%. This may or may not affect fast idle or any kind of idle???? Air Vent Cutoff Diaphram.

For parts, start with NAPA I would say.

 

This is what my car does too!