During Subaru help requests for intermittent misfires, many replies suggest checking the exhaust valve guides. For those who may not know exactly what they are looking for, I've included 3 images: good, bad, and deceptive.

Good valve guides look like this: Exhaust valve guide with no witness marks on the valve stems.

Bad valve guides can be out of position like this: Exhaust valve guide

Deceptive valve guides can be in the proper position when you lower the exhaust, but be sure to rotate the engine to close the exhaust valves of the cylinder you're having the issue with, because you may find this: Exhaust valve guide This exhaust valve is fully closed!!! The "cleaned" section of the valve stem is from the guide drifting out, causing misfire, then drifting back into position. Hence the lack of active misfire at the time of diagnosis.

I hope you find this information helpful.

Leo from Virginia

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