I have an aftermarket, bigger throttle body and sometimes when I start the car there is a hesitation, or other times it will continuously rev from like 900 rpms to like 1200 or so back and forth until I give it a little gas and then it will go to the regular idle. Can I adjust this in any way and how? Thanks in advance!

 

Have you called the company that sold you the TB? I am not certain if the F20C has an EACV (electronic air control valve), but all my previous Hondas had them. They are responsible for controlling the idle speed.