gt3civic

Since about last Wednesday I noticed that whenever I am sitting at a stop for a length of time my car idle at about 1500rpms. So its kind of idling a lot higher than the ususal 800rpm area. Also if I sit at an intersection for a length of time it seems like the rpms raise up a little bit then fall back down. Like raise to 1700 then fall to 1200. After it does the raise and fall with the rpms the gas peddle becomes really touchy. The slightest touch makes a noticeable take off and when u let off of it u instantly feel it slow down. Its a 99 civic si so I know that it does engine brake but this is much more noticeable. It really kind of jerky. It becomes kind of a pain to drive with the jerky fast/slow peddle. But whenever I turn the car off and then back on it runs fine for awhile. Does anyone have any idea what is causing it to idle so high and the gas peddle to become so touchy?