when idle.. its revs

Okay, when I first start my car.. it starts at like a high rev.. im going to say about 3 - 2.5 rpms.. but once it warms up it idle's just fine at .7

although.. once i give it some gas or start to move.. the next time i come to a stop it will sit there.. and rev up to like 2.5 - 3 rpm and then go back down to .7 and then go back up and yeah..

any idea of what may be causing this?

Iac