x351 5.0 rough idle when off AC
 

recently i noticed it idles bad when i shift to P and AC off.
i would give it a few rev and the idling usually returns normal.

this aside, can the cam phaser/ tappets/ lifters / chain tensioners caused this ? the car still has ticking noise throughout the day though it ticks less when i add the engine oil.

been to a few mechanics, all says it is not the chain noise. some say it is the tappet not getting enough oil pressure and adding oil helps (which i tried). read up a fair bit on this problem and on ford f150 forum, the possibilities extended to these parts. is there any ways to correctly diagnose the cause ?

the AC was due to the broken intake pipe which has been rectified. Plastics do break over time in this engine.