I have a 2002 Ford F150, 4.8L V8 Triton.   I am having an issue with the PATS system, and I have seen many complaints like mine on line, with no definitive fixes.  When it's sunny and nice, air is dry, it starts up without a problem.  But get a rainy day, or foggy day, the PATS warning light flashes and all she does is turn over, won't start.  Also, when I see fairly decent temperature changes,  like 90 degrees to 60 degrees, or 30 to 10, basically a 15 to 20 degree drop in temps, the same thing happens.  I can't trust it to go anywhere but a round trip without turning the engine off.  I changed out the key reader, the circle thingy that goes in the steering column, but it still does it.   Sounds like a small break or something.  I did have it start once, after the light was flashing, after opening the hood, then slammed it down, low and behold it then started.  Mechanic says it would be like looking for a needle a haystack to find it.  Any ideas?