I live on a farm and my 1997 f150 4.6 (196k) has been parked in a grassy area for the past 2 months with only occasional use. The other day it started to idle rough and stall - this was sudden, as there were no problems previously (no codes diplayed). Obviously, parking it on the grass subjects it to moisture. I've taken it for some long runs recently with no imporvements, trying to eliminate possible gas/moisture in the coils problems. I'm thinking it may be the EGR.

Any other ideas ?