I have replaced all 8 coils and spark plugs 1 by 1 in a day, #4 piston continues to mis-fire, i replaced that 1 coil and plug again, still got the same mis-fire, now the truck starts and only stays running if i hold down the gas pedal to about .5 - 1.5 rpm, if i let go the engine stalls out. I’m out of ideas, any suggestions?

It is a 1999 ford expedition  5.4  V8  automatic trans. 2 wheel drive.

Ford has at least two problems with the coils on these engines.  First check to see if there is any anti freeze dripping on the coil.  The heater hose runs right above #4 coil and if the clamp is loose or there is a hole in the hose it will drip on the coil and make it mis-fire.  Next check to see if the coil wire might be broken.  If you don’t find anything, have the vehicle scaned for any codes.  I think Auto Zone or a like auto parts store will do it for free.