Daughter's Expedition with 5.4 three-valve has had head replaced on bank 1, cam phasers replaced .... still get code for phaser (which obviously does not return from high speed operation to its low speed/idle position. Chronic... mechanics just throw parts at it nothing changes. Is this condition fatal if she just drives it and puts up with the rough running at low speed (never dies, just idles like it's out of time...which the valvetrain is). Too expensive to keep working on it, worthless as a trade in... Can she just drive it without damaging the new head?

 

Most times it is not good to operate an engine when it is telling us there is a problem.

Did anybody check the oil solenoids that allow phaser operation. Suspect there may be a problem there.