odd idle

after my car has warmed up the idle fluxuates. it will rev up 2-300 rpm and go back to normal over and over again. as soon as it returns to normal it goes up 2-300 then back down and then up, and back down, ect. the needle never stops moving. the battery and alternator are fine as well as well as the vacuum hoses. what could be causing this?

i think it has something to do with the monstor truck icon................ hehehe