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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.
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.