As the title states, #7 cylinder misfires until truck warms up, clear code then runs fine. 2005, Expy 5.4L. Does anyone have a clue why this would happen. FYI just had the COP's and plugs changed about 2 weeks ago, ran fine until now. Thinking bad COP??? not sure, guess I'll do a COP swap to see...thanks in advance

 

Could be one the new plug is bad as well. There was another thread on here a few days ago with the same issue. For him the new plug was no good.

 

Update...swapped out coil with old one I kept when did change out and presto!!! Guess I got lucky, no misfire and idles smooth when parked on the brake. Guess I'll be bringing back the "new" one to get me a newer one that hopefully isn't bad either. Moral of story, sometimes it's good to keep the parts u change out, might come in handy one day...