I leave my 2000 Excursion V10 parked most of the time, and it recently wouldn't hold the idle.
I changed the Idle Air Control Valve (IAC or IACV), which is alittle difficult, as it is on the rear of the intake manifold - but only two 5/16 bolts (atleast that fit - don't know if it was metric). These run between $50 to $100 at after market places. Autozone was $60, which was pretty reasonable.
Solved the idle problem immediately. Another suggestion was to check and clean the PVC valve. Spray it out with some carb cleaner / gun cleaner / etc and see if that solves the problem.
Cheers!