Verified answer

This problem plagues owners of various models year between 1995-2010 of F-150s and crown vic/marquis/marauders. The EATC module is a vacuum-powered head unit right behind the front cover of the dash (very easy to get at in 2-5 minutes.) There are 4 tiny little o-rings on the solenoids in this package that start leaking intermittently after a few years with strange results as you describe, then they just get worse. On my 2007 MGM they went last winter, but I think being in Florida heat accelerated the failure.

Anyway, you have 3 options: 1) Get a whole new EATC module for about $250-500, 2) send it away to one of several outfits that offer a rebuild service for about $100-150, or get the o-rings for about $2 and change them out yourself. Click the links for pictures and/or a very detailed break-down of the procedure. If you want them to last forever use new o-rings made of viton rubber, but since yours have lasted over 12 years you might go with neoprene again, which is what you'll find in the o-ring section at Lowe's, ACE, etc. I skipped the grease but paid a little more for a bag of 25 viton o-rings.