So quick summary; when I bought my '03 G35 Coupe it had a SEL and two codes. One was a high idle (can't remember the code) and P0327 which is supposedly the knock sensor sub harness. After I did the idle relearn; the car idle smoothly but the SEL remained on but I knew it was the P0327. Fast forward a week and the SEL goes off completely.

Here's where my question comes from. When I use my OBD scanner and scan for codes using the Torque app the P0327 shows up but as a "pending fault". Did the code get fixed after I fixed the idle?

Since I'm about to swap out my valve covers because of an oil leak into my spark plugs; I was wondering if I should buy a new sub harness and swap it out since I already have the engine apart.

The p0327 code could also be the knock sensor itself not just the harness/wiring. Most likely you have a bad knock sensor.