Yeah, it's a 5.0 with EFI; looking from the front of the vehicle, the idle screw is just to the left of the air filter box, and just below the aluminum intake. On mine it's behind a couple of sensor wires. Clockwise will increase the idle.
I'm sure there are some sensors that are dying, or maybe the cumulative effect of age on all that electronic stuff. That's why you'll see original 60's cars, but hardly any early FI cars...all the electronics die and you can't fix it without selling your house.