2009 Forester XT - misfires P0301 and P0304 - changed plugs, coils and O2 sensor - no fix. Whats next?

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I have a 2009 Subaru Forester XT with 240k miles on it. I’ve been having an intermittent CEL and P0301 / P0304 DTC codes for quite awhile, recently it’s gotten worse.

I’ve replaced plugs and coils. Denso coils and NGK Iridium IX plugs. No resolution. The 4th cylinder seems more common - with 1st cylinder occurring at about a 1:4 ratio (ironically) of how often.

Worth noting is that I previously had an O2 sensor code as well and replaced that - haven’t seen this code since.

The CEL flashes typically at low idle and/or when under load at a stoplight. It’s very noticeable and constant when around 700-1500rpm - while in gear and brakes applied. If I shift into neutral and let go of the brakes it’s much more subtle.

When over 1800rpm, I rarely feel a misfire and have yet to see a code trip that I can recall. 2000+ rpm in neutral feel smooth. When on the freeway at approx 70-75mph it seems to jerk and/or hesitate sometimes. But at speeds above or below - it operates fairly smoothly. (Might be completely unrelated)


What should I be looking at next? Is there anything I can double check rather easily / quickly? I have an ODB (Bluetooth / phone) and a fair amount of tools - voltage / continuity tester, etc. Logic seems to point to fuel… but maybe over looking something.

Happy to provide any other info / details. If this is total rabbit hole and we’ll worth taking to a mechanic, let me know - but I’m pretty cost conscious and feel like I should be able to figure this out.
 
Vacuum leak? EGR, Brake booster or PCV, Oil leaks?
Compression test on all cylinders? Fuel pressure? Fuel flow? Fuel quality?
Dirt in one or more injectors?
Coolant leak into one of the cylinders?
Battery and alternator output within specifications?
Ground straps in good condition?
 

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