new to Subarus and this forum, I just replaced the MAF meter so I'm back and running, two codes left are P0325 and P0400, anything i should know (like where the knock sensor and EGR valve are located is a good start), any methods to test them , thanks

The knock sensor is just behind the intake manifold on the drivers side. Look straight down, it's black about 1.25" in dia and has a 12mm bolt.

 

There is an ohm check you can do for resistance.

 

The EGR is also on the manifold, drivers side. With the car running, pull a vacuum and if the idle changes, the valve is clear. Lots of times the valve or line from the cylinder plug. Start with cleaning them if necessary.