I own a 2008 Fit with a manual transmission it currently has 206,000 miles. Haven't had any major issues other than the usual items. Recently I did get a p302 code which for some reason will not go away. Started with replacing the spark plugs with Ngk iridiums no change then replaced all the coil packs with original equipment no change then adjusted the valves again no change. Check cylinder compression that was all good. Replaced both upper and lower 02 sensors again no change. Switched the coil packs around still no change I even put in a new set and again no change. Am I missing something or is there something else I should look at?? Could the ignition harness be faulty??

 

Are you using Hitachi coil packs? Fits (and other Hondas) are super picky about running non-Hitachi coils.

Are you using authentic NGK spark plugs of the factory heat range or one step colder? There have been many counterfeit NGK and Denso spark plugs being sold via Amazon and eBay. It is encouraged to get them through known good/trusted parts venders.

Did you do the valve adjustment with the engine cold and double checked your work after doing one full engine rotation?

Do you have a scan tool that you can see misfire, fuel trim, and MAP sensor data as well?

The L15A in the first gen shouldn't be too hard to get sorted. I was in a similar boat when buying my at the time 348k mile daily beater GD and the previous owner did some rather... questionable and sparse maintenance. lol