When engine gets hot, idle is up and down with the engine light on. OBD code gives a P0505 code.

That code is for the idle speed control valve. Please follow the link P0505 Honda Idle Air Control Valve

P0505 - Idle Control System Malfunction P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

All you need to do is use Google

Type: 1997 Honda OBD PO505

OBD -- before any code, will give you
hours of reading & studying on the internet

P0505 14 ICS Malfunction
http://www.ericthecarguy.com/29-obd-codes/obd-ii-codes/honda-obd-ii-specific-codes/215-p0505-idle-air-control-valve-malfunction-honda

p0120 means you have a throtle position sensor problem could get expesive if throtle body is bad p0505 is same problem it means throtle idle controle valve problem hmm short bad ecm or bad throtle body hope this helps

P0505 - Idle Control System Malfunctionhttp://engine-codes.com/p0505.htmlForum CodePossible causes- IACV-AAC valve harness is open or shorted
- IACV-AAC valve poor electrical connection
- Faulty IACV-AAC valve

Read more: http://engine-codes.com/p0505.html#ixzz1zVJIt34L

P0505: Idle Air Control Valve System fault, Code P0505
-Vacuum leak
-Dirty throttle body
-IAC motor defective
-Poor electrical connection to the IAC valve, hope this helps and good-day !

P0505: Idle Air Control System

There is a small motor that controls the amount of air the engine gets when you aren't using the throttle. The computer uses this small motor to control your idle. It sounds like it needs to be replaced. You can try cleaning it first with some throttle body & air intake cleaner.

Get a can of carburetor cleaner and spray it into the throttle body while the car is running.

There is a small electric motor call IDLE AIR CONTROL (IAC).

It add rpm when there is load like headlight,radio,power window while you at idle.

Just to bump up the power a little to keep everything operate smoothly.

When IAC is not functioning it will give you uneven idle.

Get the OBD-II code and repost. It will help you to get to the real problem.

OBD-II connector is 18" from the center of the lower dashboard. Scanner is about $50 to start.