I have a 93 Honda civic. When i start my car it starts reving from 1000 to 2000 constantly. I've checked my IACV and thats not it. When i unplug my Map sensor and restart the car it stops that problem but gas mileage is really bad and it runs really rich. I don't know what else to do.

 

start here, it's helful
http://www.ef-honda.com/ben/Badidle.php

 

its your fast idle valve on the bottom of the throttle body...you have to screw the plastic spring cap back down on the inside of it....this has been covered a thousand times this week....search.