So I have 04 with 5.4 that vibrates upon acceleration once it's up to speed 50mph+. It only does it after it's at speed and I let off the accelerator and then re-accelerate. Has new plugs and coils installed already. Help please!

 

Well plugs were supposedly changed 6k ago. Pulled them out today and think previous owner got hosed! #6 didn't even have the metal piece on it to spark to. Runs good now. Thanks!

 

Glad you got if fixed! No telling who is lying there unless the PO has a receipt. I might be wondering if the cops were new. I recently watched a youtube mechanic video where this car was missing. Supposedly had new NGK iridium plugs bought off amazon installed by the owner a few thousand miles before. The problem was the electrodes were almost gone. So, the owner got some chinese fakes off amazon.