We have changed the serpentine belt and the idler tension pully and the belt still keeps walking off. What else could be wrong?

Aaron did you recheck the belt tension within 30 days after the installs?Me personally I pop the hood an have look see make sure it won't fly apart on me !

Failed Water Pump

Crankshaft Damper Worn

Failed Belt Tensioner

Failed bearings in any accy

Possibly, I would check alignment of the pulleys, they should all be on the same plane. Run the engine and watch it.

COULD BE A BAD BEARING IN THE IDLER PULLY OR THE TENSIONER ON THE TIMING BELT OR THE SERPENTINE BELT. IF ITS A SQUEEL IT MAY BE SOME COOLANT GOT ON THE SERPENTINE BELT. TRY TO WASH THE BELT WITH WATER AND LET DRY COMPLETELY. IF NOISE REMAINS RETURN TO THE SHOP THAT DID THE WORK.

Your tension spring is shot. purchase a new idler pulley and tension arm bracket. that should fix it.

check your tensioner and idler pullys for free movement. then check all your accessory pullys for operation. if that all checks out then it was just a defective belt

Really don't need a diagram. Loosen the slide bolts on the power steering pump. loosen or tighten the pump by turning the jack screw (long transverse bolt) under the pump. Once the belt is tightened up, lock down the slide bolts and you are finished.

It should not require any adjustment. the right tension is provided by the idler pully. If you want to release the tension for serpentine removal or examination release the tension on the idler pulley in the rear of the motor, spin the nut in the center like you were tightening, and the pressure will be released from the serpentine belt. Reversely, the appropriate tension will be given using the same way when the strap is reinstalled.
Dan

first thing you need to do is get a new belt that belt dressing just destroyed that belt that stuff is no good then get a new belt tensioner clean all the pullys with some brake clean then install the belt tensioner and belt if its still sqealing there maybe a pully making the noise to check that when you have the belt off spin them by hand and listen to them and feel for any play in the bearings

Just to make sure you have the right part (belt Tensioner), If you push and pull on the serpentine belt, look for the pulley that moves with the belt. That will be the Belt tensioner pulley, there is going to be a slot on the tension arm for a ratchet so you can take the tension off the old belt and slid it off the idler pulley or any one of the other pully's. Good luck and hope this made sense, keep me posted be glad to help.