So I recently bought a stock 2002 WRX with 145k, this is my first subie and I'm really new to working with cars. It's giving me a bunch of different misfire codes ranging from P302 to P302-3 and even P302-3-4 or P301-2-3. The idle seems fine, it stumbles a very small amount every now and then but nothing I would consider out of the ordinary. I am getting inconsistent boost at higher RPM ranges though. It's like the boost will surge then die down then surge then die down again but in rapid succession. The CEL that comes on doesn't blink and going into high RPM ranges doesn't trigger it. I've done a few things to try to fix the issue already which I will post below. I'm completely stumped on this and I would seriously appreciate some help. Thanks in advance guys.
Replaced spark plugs - NGK Iridium
Swapped coil packs
Cleaned fuel injectors
Replaced fuel filter
Replaced crankshaft position sensor