Had this one time, codes 300 and 30X's popping up after steam cleaning engine... was water in plug boot/s.
Figured it out after trying trouble shooting the coils, swapping in a new one I had, electric contact cleaner on connections, etc.

The plug boots had dielectric grease in them but still got wet enough to cause misfire.

I now blow dry motor after washing getting around plug boots and coil pack connections with compressed air.
Helps to use good quality plug wires!
... and if I recall it was both boots on cylinder 1 had moisture fwiw.

(pulled them off blew out with air and regreased to the max and made sure they were seated in all the way,,, maybe not clicked fully on the plug and boot wasn't maxed out so they got moisture in? IDK)

Then no codes, no stumble, ran great.
Cheapest fix there is....AIR