PLEASE HELP! Idling and Stalling Problem!!!

In my 2000 Buick.. When I turn the car on and leave it sit for a minute the RPMs start jumping and then it just stalls.. When driving it seems fine until I slow down to stop and then it stalls again.. I NEED HELP!!! i have no idea what it could be.

Have you had codes pulled yet? Autozone and other similar shops will do this for free. That would be the first place to start as there are just too many unknown variables otherwise.