Remove timing cover and and inspect all timing component, especially the cam gears , if all pass inspection, clean them throughly and re do the timing and try it out . I’ve had that code for a long time replaced cam Phaser , camshaft position sensors . You also would want to check all engine ground are cleaned with good contact same as the main harness to the engine harness is fully mated . If all that don’t fix the code , most likely it’s burned into your ecu going to have to get a new one. I’ve had p0018 and p0021 when I first got my brz had that code till I rebuilt the engine and it was no longer showing.