My pressure regulator was replaced along with fuel pump & fuel filter this code keeps coming back. Sounds strange at idle while in gear at a traffic light.

Ok I was told by a shop I need a new cam shaft and HPFP, so I decided to pull the HPFP check the cam follower it could be replaced but wasn't destroyed the lobes also looked good. I have one and will replace it... Don't see anything obvious with the HPFP , I will replace the fuel filter. I can tell no one pulled my valve cover to check the cam, not sure how they diagnosed this without physically checking .