UPDATE:

had a valve adjustment done. 1 and 4 were a little tight. There is carbon on the valves, but no burnt valve.

Any tips on cleaning as much of the carbon out as possible? The guy in the shop said that there are little mesh pieces that will make it impossible to clean out all the carbon, but if anyone has any tips I'd take them.

Weirdly, the valve adjustment has reverted me back to more pronounced misfires during freeway driving where I can feel my acceleration briefly due and then come back a few seconds later.

ORIGINAL POST:

My Element has treated me very well over the years but recently it's been having some kind of engine problem. Trying to just narrow it down as to what it could be.

The codes I'm getting are the dreaded P2646 Rocker Arm Actuator Stuck Off Bank 1, and P0304, Cylinder 4 Misfire. I also have a broken knock sensor, code P0325, but that one seems cut and dry -- replace the sensor, solve the code.

The two symptoms I notice most are that the car seems to "breathe" when I am at a light or in a drive through. You can see the RPMs bouncing up and down and hear the engine revving and slowing a little. At one point I even felt it moving a tiny bit when doing this, as I heard my brakes squeaking as it tried to pull forward a tiny bit.

The other one is that it is struggling to go into 4th gear. I can feel a sort of fog over the acceleration when driving it, like it can't fully accelerate like it used to.

We have recently completely replaced the VTEC oil sensor, hoping it would resolve the Rocker Arm code, which lists a faulty or malfunctioning sensor as a potential symptom, and it's been mentioned in the past. I felt like that improved performance some. It's also had oil and filters changed, as well as plugs and coils replaced. I read online that valve adjustment might help too, but we haven't tried that yet.

Any tips? Or any further info I could provide to help narrow the core problem down?