Engine cam code p0021?

I thought the problem I had with the mess while driving was solved by replacing the plugs, but it came back. So, it seems to only happen when the car is cold. No lights on the dash until this happens, feels like you almost out of gas, couple of hiccups, never stalls or shut off, traction, brake, ABS, and check engine lights all come on. I scanned it and the brake lights came just due to the mess from engine, so it is not it. The engine came with code p0021 for cam. Any suggestions? And where is it located? is it one on passenger side by front of the valve cover? this engine has so many sensors it's hard to pinpoint it.