Idle problem

!995 honda accord, 5 speed. Idle is fine until the engine warms up, then fluctuates between 1500 to 2500 rpms. The idle control valve was cleaned- no change. Valve was also replaced -also with no change. Put old valve back on. Computer was disconnected after cleaning and also after each valve change.
Would the next step be to remove and clean the fast idle thermo sensor? Also how do you check the coolant lines coming in.
Does anyone know of anything else I would need to check, clean or replace.

Has the thermostat been changed?
Has anyone done a thorough check for vacuum leaks?
Those two things should be on your to-do list, IMHO,

I can think of two more things, the throttle body is dirty so the throttle (butterfly) doesn’t completely close or someone has fiddled with the throttle stop screw.