I have a '98 f150 with a 4.2l/5spd. For some reason whenever you put much of a load on the engine especially in 3rd, 4th, 5th gears) it will miss/sputter once or twice then take off again and run smooth. I changed the plugs and wires about 20k miles ago and that fixed it for a couple of weeks then it started doing it again so i took it to Ford. they changed a plug and once again it ran fine for a week or two and now it has been doing it for about a year. Any advice? Also im gettin not-so-great mileage 14mpg hwy the engine just rolled over 80k and has not been "hot rodded" do these engines hold up pretty well?

 

If you get a stutter just as you move the throttle and it only lasts 1/2 second or so, it might be the TPS. That'd be the cheapest also.

 

Check your coil if you are having misses and buring plugs it is a possibillity that your coil is going south. Have you done the regular maitence as well Filters etc.

 

the truck has been well maintained, new oil and filter every 3k or less miles.