Number 8 cylinder misfire

Check the plug check the coil check the coil wires

Check the plug check the coil check the coil wires, best way to do that is a swap the wires from #8 with the cylinder next it. Then you see if the code from the check engine light follows the coil or stays with cylinder 8. Good luck!

Put in new coil and plug. Still reading #8 cylinder intermittently

Either 1) clogged / broken fuel injector or 2) bad / corroded coil wiring harness. Good thing you replaced the plugs and coils first, since that's usually the easiest-to-fix cause of a misfire. Since its not that, I would run SeaFoam through to unclog all your injectors anyway, and see if the misfire occurs after the unclogging. Next, replace the wiring harness / wires to cylinder 8, as that will be cheaper than getting a new fuel injector. Hope this helps!