Got a buddy with a 98 white f150 with the 5.4 motor. It will start up & idle fine but if you try to drive it it has no power what so ever.

If you can give me some ideas of what it could be?

 

Are you sure it's the motor, or could it be a tranny issue? Is it auto or manual?

 

In this order,
Check for codes,
test fuel pressure for being in the 30 to 40 psi range.
If nothing found, it's time to put a Scanner on and look at live data for the problem. It will show some where in the data.
Don't replace parts trying to hit it until something is showing as faulty.
Good luck.