A prolem with this honda is after warming up the idle goes up and down while at a stop.

You shold take to a mechanic and they can re set your idle, but something else mybe wrong!

. Clean/replace the Idle Air Control (IAC) Valve.
. Ensure all vacuum hoses are tight.
. Ensure spark plugs have been replaced in the last 24,000 miles or 2 years.
. Check idle speed:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563.html#post219948

. Check engine timing:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563.html#post219963

I had the same behaviour on my 1989 Honda Accord LXi - rev up and down when warm. Very annoying. But the fix was easy:

What you most likely have is a dirty IACV a.k.a. Idle Air Control
Valve that causes this. The sensors there can get dirty sending erratic signals. So I cleaned it without even uninstalling the thing, just loosening the two bolts and using a straw from the spray cleaner to get inside and in between the crack to clean the sensors and viola, the engine runs like new.

Just be prepared for the rubber gasket to fall out. You'll have to fish it out and place it back as best you can before tightening the two bolts again.

Here's more on this issue:
How To: Clean Your IACV - Team Integra (http://www.team-integra.net/sections/articles/showarticle.asp?ArticleID=1174)

Here is a suggestion start with the vacuum Control Box..

I also found that if the water level in the radiator is to low, the motor will idle up and down. When I topped up the water level, the idling returned to normal. That was after it started idling funny again later, after I had cleaned the Sensors.

Since that is the easiest thing to do, I'd check the water level first.