About a week ago, I started getting a bad hesitation being idle on the gas at about 48 or 49 mhp.. I figured a misfire and that a tune-up would solve the problem. As I drove on it for the remainder of the day, it got real bad. It started to do the same things at higher speeds, around 64-65 mph./73-74 mph.. But at lower speeds (under 40) I had no problems. Then as I was taking it to my local mech., it started really going crazy. It was shaking the whole truck. Sitting idle at a light, driving at 15 mph., or 60 mph., it didn't matter. The only time it wouldn't give me the jarring shakes was when I would slam on the gas, she would take off like a rocket. I got it to my mech. and had him run a dio. on my truck, no codes what so ever. After thinking about it, my check engine light never came on either. he went ahead and gave her a tune-up, changed the oil, and a 3 step fuel induction. He called me up, said I was good to go, and should have no problems. I trust this guy beings that he has worked on every truck I've owned. My truck ran fine for about 2 days, then it started doing the same thing again. The shaking isn't as severe,yet. I called my mech. back, but he has no clue either as to what the problem could be. If any body would have any ideas, it would be greatly appreciated. (side note: I now own a 2000 F-150, 5.4 V8, K&N air filter, super cab, 4x4. I owned a "98" F-150 before this one and had the same problems, sold it before putting any money in to it to try and fix what ever was wrong with it. My uncle also had a "98" with the same symptoms. He ended up having to replace his whole fuel system. {lines, pump, filter, injectors, etc.}

 

My '02 5.4 was having the same problem. The dealership attributed it to the spark plugs...a mis-fire on 3 and 8. I am going to go change both plugs and see if it fixes the problem.

 

Misfires are very deceptive. The CEL doesn't always come on when they are detected. What all did the 'Tune-up' consist of? My most educated guess is that a plug is bad.

 

I had all the pluge changed, and had all the coils checked (all were fine). I also pulled all the wiring harnesses away from the a/c accumulator-drier. I read a few other posts that suggested doing that. Other than that not much has been done. Any other help would be appreciated.