1997 Prelude - Low idle problems

My 97 Prelude idles fine when cold, and runs great while driving when hot or cold, but if it is warmed up, it idles to slow, and when the A/C is turned on it idles so slow that it gets very rough and sometimes sounds like it is dieseling. It has had regular Mntc by the book it's whole life and now has 117,000 miles on it. I already cleaned the IACV sensor, but it wasn't dirty. With the engine idling, I unplugged the IACV, and when the AC kicked on, the engine almost quit, until I plugged it back in, so the IACV seems to be working. I don't know where to turn next??

Thanks,
Baffled

Have you tried adjusting your idle speed on the intake manifold? Make sure the car is warmed up when doing so. Also, if that fails, move the distributor a very little amount and that'll increase the idle.

This Prelude is completely stock and has always ran great, therefore, the idle screw has never moved and neither has the distributor. Changing them now would only cover up the root cause, which must be one of the engine sensors. This is basic stuff for someone who works on Hondas all the time, which I don't, so I thought some experienced Honda Guru could tell me in a heartbeat which sensor to replace. The purpose of the IACV and the IATV is to control idle speed under changing conditions. IATV bumps idle up when engine is cold, this works great, and I verified the IACV is working when I unlpugged it, ran the AC and plugged it back in. I'm sure there must be other sensors that have an effect on idle also, that is what I am looking for.

Thanks

Is your Check Engine light on?

Check engine light was not on, until I temporarily unplugged the IACV, but I have since reset the check engine light.