I also cleaned off/out all the COPs as well as the spark plugs. Two plugs took some penetrating oil and a breaker bar to get loose. I sanded down the surfaces on the ground electrodes of all the plugs. I put a bead of dielectric grease around the sealing surface of the COP where it meets the valve cover and also put an insulating bead on the insulator of the plugs. The #1 cylinder plug had some small cracks on the insulator, but I put it back in anyway. I'll replace the plugs and O2 sensors at the same time.

 

Pending codes are caused by intermittent faults or faults that the PCM needs to see happen in two consecutive warm-up cycles to set the code.

 

Your explanation makes sense. Now the codes are popping up fast and regularly. P0136 and P0137 codes.

 

I re-installed the factory intake baffle and intake tubing to see if my DIY CAI was causing the P0136/P0137 codes. With the factory stuff on, the P0136 took a long while to come on but it did end up coming on. I plan to drive it again tonight and tomorrow morning to see if the P0137 comes back before re-installing my CAI tubing.