I have a 2000 Taurus. I'm losing my power steering at an idle. as soon as I rev the engine I have power steering. Is it the pump?

Could be pump, could be belt slipping, possibly bad tensioner.

If i were you i would start by checking the power steering fluid, make sure you have the fluid in there, next the tensioner, then if that is all good, it probably isnt the belt slipping because then it would be burning up, since you have no power steering that would mean the belt would have to be slipping so much that the belt wouldnt be powering the pump, so your belt would literally burn up, so if the tensioner is fine i would say replace the pump.