2001 Altima idle racing when car is stopped

When at a light or stopped with the car in drive, after 15 seconds or so
my idle starts going up and down almost causing the car to leap forward
if I didn't have my foot on the brake!

Has this happened to anyone and if so what is causing it?

My 2001 Altima SE hesitates when the car is idling. The rpm will go up and down erratically between 300 and 700, but the car doesnot stop. No Check Engine is coming.