You can't leave the cpu without fan. If it is faulty (stuck or revving slowly) it must be replaced. You can repair a fan by dismantling it, remove the sticker that covers the bearing, oil with WD40 or another cleaning/oiling agent, rotate it nanually until free and cover again with a sticker to avoid dust from coming in. If the fan is in really bad shape, however, it will start giving problems again. Whenever possible I prefer a new fan.