1992 civic automatic idles okay when cold engine, but idle fluctuate 800 to 2500 RPM when engine hot

old post.
too fast hot or cold.,
this car has a ECU, brain,
the brain controls RPM full time hot,
not you unless you step on the throttle.
only IT does. the ECU.
if the idle is wrong when cold engine, that is the IAC failing.
or is normal, I dont know you never stated
hot
cold
or and RPM

turn idle screw down. this car may have an electric or vacume controlled idle. get a new motor for it. look on the throttle plate to make sure the cables are on correctly

clean throttle body,and check for vac leak

Engine stalls cold or RPM fluctuates at idle up and down or dies near idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve but always run a OBD2 fault code as well as the cleaning procedure. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control. If the above cleaning doesn't cure your issues you need to have the computer controlled automatic idle speed control system diagnosed and repaired by a dealer or electronic engine control repair shop.

Engine stalls cold or RPM fluctuates at idle up and down or dies near idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve but always run a OBD2 fault code as well as the cleaning procedure. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control. If the above cleaning doesn't cure your issues you need to have the computer controlled automatic idle speed control system diagnosed and repaired by a dealer or electronic engine control repair shop.

Engine stall or RPM fluctuates at idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

Is it actually hot the radiator Imean. If so check thermostat ,coolant level,of both ok than faulty guage.

the speed sensor on an automatic is located on the back left underside of the transfer case (transmission). It is held in place by one 10 or 12mm(I believe) bolt. Sorry no clue about the idle sensor.

Make sure your anti-freeze is full in the radiator.. If it is low, the heater is the first to go, but you wont see signs of overheating.. This I believe is also contributing to your idle fluctuation.

it might just be your timing i had the same problem with my 94 hatch did have any power on first or second just had a friend adjust the timing and werks just fine.