Won't idle: UPDATE

Helping a friend with a 2000 Recon he just bought.It's in pretty rough shape but supposedly it ran well when it was parked two years ago.It will idle at a decent speed for a while then all of a sudden the RPM's will increase just like you're pressing the throttle.If you turn the idle speed down it's o.k. for a while then all of a sudden it will sputter and stall(cause the idle is now too low)The tank was drained,carb. was cleaned and blown out with air,the vent hose is open.What else is there?
LAST NIGHT I REMOVED THE CARB. AND CLEANED IT OUT A SECOND TIME.PUT IT ALL BACK TOGETHER AND IT'S WORKING PERFECTLY.IT LOOKED PERFECTLY CLEAN,SO I DON'T KNOW WHAT CAUSED IT