my stepdad has a 95 F150 reg cab/long bed with the 5.0. he's been having a problem when it rains out/snows/ or there is heavy moisture. when you are stopped at a light at idle it is fine, however in the low revs just above idle (when you first step on the gas) it runs very rough until you step on the pedal, then it goes away. Any ideas

 

At night when it is dark out lift the hood while it is running and see if you see sparks jumping around just above idle.
If you do not see any try spraying a little water from a spray bottle around the spark plug wires and cap and see if it dose it then.

It sounds like bad spark plug wires or the distributor cap.
You could also check the gap on the spark plugs and see if it is right.
The gap should be on the plugs .52 - .56.
The plug type should be ASF-42C.

 

Spark getting sidetracked before reaching plug is a good bet. a clogged air filter works worse w/ moisture laiden air. Run the scans. You might turn up Low flow EGR or MAP sensor out of range. 2/3 can of "Seafoam" thru air intake & 1/3 in tank might prove helpful including w/ tank condensation .

 

I'm kinda new here, but my 95 F150 5.0 liter doesn't have a MAP sensor....at least not that I've been able to locate. It does have a MAF sensor mounted in the air intake tube. Just thought someone should know that not all 5.0's have a MAP sensor. The MAP is supposed to be mounted on the a/c condensor by the firewall but not on my 4x4. I'm guessing some models have MAP sensors and some don't. Your problems sounds as if you have a crack or fault line in your dist. cap. Sometimes you can't tell unless you check with a strong light or a good cleaning. Anyway, hope some of this helps.