I have a 2001 Expedition with the 5.4..a few months ago I was having an AWFUL bucking problem, we did everything to fix it from new coils to new plugs, the TPS, the EGR, PCV, checked for vacuum leaks etc...we replaced the plugs twice which seemed to solve the problem..BUT (Always the "but" that gets ya) after doing all of that it threw the p0171 code, but the truck was still running pretty good, I bought a new oxygen sensor and put that in...and this is where it all goes down the tubes...almost imediately after putting the 02 sensor in it was idling awful...then driving it it sleemed to have a slight bucking, stop at a red light and it seems like it is going to stall but then catches itself..

Yesterday I had to drive about 60 miles, mostly highway, and then 60 miles home, on the way to my destination it ran o.k., not great, but o.k., however on the way home it was just terrible...upon starting the truck right away the idle was so rough it felt almost like a hot rod..I proceded to "rev" the engine and it seemed to fix it...I put the truck in gear and drive, seems o.k. (again not great just o.k.) Until I get on the highway...when I tried to maintain speed is when it seems to buck, once it bucks I put the gas pedal to the floor it didn't hit passing gear just accelerated very slowly, then kinda hit passing gear, then the truck runs good for a few minutes..until I come to 5 O'Clock traffic..stop and go, stop and go, everytime I'd stop it would chug and almost stall, I kept my left foot on the brake and right foot on the gas to catch it if need be (didn't wanna stall in the middle of interstate 95) I get the truck home, pull in the drive come to a stop but still in drive and for a split second it wanted to stall but again didn't...What in the world could this be???? I have changed everything I can think of, I think all that is left is the IAC? Could this cause these problems? We re-checked for vacuum leaks and cleaned the MAF and throttle body as well and checked to see if my cat is glowing, Oh I also took it to Ford to have it "diagnosed" and that got me absolutely no where, they told me to replace coils # (what ever ones they told me to replace I did) but it didn't help.....

Any suggestion would be GREAT as I am supposed to be leaving in 2 weeks to go camping and need to pull my camper ( oh and take it easy on me cuz I'm a girl, lol) Thank you everyone is advance