What would make a clean "eat off the motor" 2009 Expedition 5.4 gas engine go from "perfect" to sounding like a deisel with a miss?
Details:
Revs up fine in idle/park.
Runs rough on the road with no power.
The change happened in a moments time. Just drove 600 trouble free miles over the weekend. New oil change right before we left for trip. Before we drove back I used 93 octane because I found out my wife had put 87 in it before we left...but everything still ran fine there an back. It sits over night and on a 3 mile run to the store it just rattles and gasps but revs up fine still rattling a little. It seems to be getting enough fuel pressure from pump. It doesn't stall...just sounds crazy...like an older ford with a vacuum hose off or something. I've looked all over for anything outta place ...Is it a coil pack? I'm lost please help.