today i started my day by running errands, probably was driving around for like an hour or so...and the idle was fine. then i went to fill up gas, and like 5 minutes later everytime i took my foot off the gas the car would idle like at 1200, then start bouncing up and down between like 15-1600 and 1000, up and down, up and down...kinda fast too. it would bounce maybe 6 or 7 times then settle around 1100 or so. i would push gas and start driving again, and when i stopped it did it all over again. it's very irritating. what could possibly happen that quick that would cause my idle to just get all funky like that, and what can i do to fix it?