i have been noticing my car has been idling a little funny

when i let off the gas and clutch in the idle drops all the way to like 600 rpm and then back up to 1200. somtimes when i am at a light i notice the car will go from 700 ~ 1200 rpm back and forth for a few times. what might be causing this? thanks

 

check your idle air control valve or see if the fast idle is gummed up.

 

from what i understand so far it does it only after the engine has been driven for a while? would burping the radiator help?