It could be a multitude of problems.
- cam sensors marked with a "D" were bad from factory
- Oil Galley bolts loose, behind the cam phasers on the front of the valve cover
- will cause worn valve guides on the front, listen for an engine tick at idle
- and even the head warping and causing even more trouble.
- cam phasers themselves could be loose too.
Some diagnostics can help narrow down the problem.
- if a new sensor is not fixing it
- check the thing that it is sensing
- check the wiring back to the computer
I did these diagnostics on the passenger side cam sensor and found a broken wire inside the plastic sheath.
Edit: some more quotes
If the cam sensor is stamped with a part number that starts with "D" it needs replaced. (TSB 18-054-14)
There is a (TSB S1618000050) for the oil gallery bolts getting loose. This can lower oil pressure to the cam phasers and valve train, which could cause some big problems in time. Just pop off the valve covers and tighten the two bolts on the front of the head behind the timing chain phaser, to 9 ft/lbs. (Oil control valve 110ft/lbs)
There is an extended warranty (D-14-12) for heads that are labeled "AB" if they warp and burn out the first valve guide, causing all sorts of damage, and sounding like a tick. Head casting marks right above the exhaust pipes 2062X and lower.