You might want to check the fuel pressure. I have seen a few P0300 that were a result of a weak fuel pump.
On older cars, this was easy... However since Nissan/Infiniti moved to a return-less fuel system it requires a special tool.
You can pay someone to do this, or buy a "fuel tap" and 60 or 100 PSI gauge.
This is the one I use:
https://cj-motorsports.com/products/fuel-tap-npt-2-bolt.
What ever you decide to do, the fuel pressure should be 50-51 psi at idle.