I have had a Mazda CX9 GT, 3.7L, 2009, bought second hand with 87k mile. A couple of times I have had the CEL come on and off. Using a reader I get a P0012 & P0022 codes. Also there has been an abnormal knocking sound from the engine right side before the last oil change, with intermittent retarded acceleration. I changed the oil and resetted the CEL, but no change. I am not a mechanic but an enthusiast. Please can someone enlighten me on the possible issues? Thanks in advance.