Hey guys, I have a 1998 ford F-150 4.6l 50th anniversary edition with 47380 miles on it. This is not a normal every day work truck, I bought it in the summer of 2006 with 45455 miles on it and it has been garaged for the past year and a half. Yes it does sit most of the time and I think that is the problem. Well today I decided to start it up and pull it out. So it started right up with the brand new die hard battery in it that I installed last summer with 725 CCA's and pulled it out. It squealed a little and the engine warmed up and it sounded like an 11 year old truck with low milage that sits alot warm up and idle. I noticed that the engine would idle normal go up a slight bit and go down, it did not do this constantly but every so often it would idle nice go up and right back down again to a nice smooth idle, the tachometer did not move at all, no accessories were on not even the radio and as the longer the rig idled the less it would do that, so it was much smoother at 45 mins of idle than 20 mins of idle. What you have to understand is that I may be only 20 years old but that truck is adult driven, I drive it like a little old lady drives a buick it has never been beat on, the only time the pedal hits the floor is when I feel I must blow the carbon out of the engine. To be honest with all of you I think it is just because it sits for so long and I only let it idle for 55 mins, I did not drive it at all. I just wondered if any of you have had this problem and know what it could be it does have original everything from the plugs to the brakes. I was thinking vacuum leak but all the hoses and clamps are tight and again it was not constant. what do you guys think.