Sounds to me like the lower trim piece, normally held inplace by 7/32 bolts. It covers the underside of the front end, from bumper cover and radiator / coolers to under the belt.
When I installed my Procharger I was surprised to find most of the screws that were supposed to hold it up were missing. Think I only had 2 of 6 left or something like that.
That is the part I'm talking about but if it's called the lower trim piece? I can't find anything on that or on the Air Diffuser on ford.com