my dad has a 97 f-150 xl with the 4.2l motor.. anyways heres the problem any time you start the truck up and leave it to idle the idle starts going up and down and gets worse and worse untill it falls on its face everyone said it was the idle air control valve so we went out and replaced it and still no fix if anyone could help me out it would be great.. thanks all
-John

 

I think this may be what your looking for:

https://www.f150online.com/forums/sh...*&pagenumber=1