High Idle
 

1997 Civic EX 4dr Automatic 178000 miles

After I have driven for awhile the idle wont drop down. When I am in park it sits a 2000 rpm. I know some honda have an air valve, or something, that you can adjust. Does not matter if the a/c is on or off.

Also the idle doesn't kick up when the a/c comes on.

Any help would be greatly appreciated.

First check is to make sure the throttle cable goes slack and the throttle plate closes all the way when no one is pressing the gas. I think your model has a fast idle thermal valve on the thermostat housing, it is plastic and easy to get broken off. Take off the idle air control valve from the bottom of the throttle body and clean the air passage with spray cleaner.

This is a MAP controlled system, so basically air leaking into the intake from anywhere will cause idle speed to increase.

That was the problem. I tightened it awhile ago and i did it too much. I backed it off and it went back to normal. I don't like a lot of slack in my throttle cable. All is good now. Thank you.