Sputtering at Idle

I have a 1995 oldsmobile cutlass cierra that is sputtering when I sit at idle for too long. It just started happening about a week ago but it seems to be getting a little bit worse each time I take it for a drive. Does anyone know what could be causing this problem? I would like to keep this car around till at least 300,000 miles and it only has 30,000 more to go.