Hello. Recently I started having issues with my 2008 grand touring. I left for work the other day and it was very rough and had little power. The check engine light started blinking, I returned home as I was not out of the neighborhood checked fluids and everything was fine. Started it back up and it was fine check engine light was solid but car ran fine. Ran the CE code which was P0304 missfire in cylinder 4. No more issues the rest of the day so we replaced spark plug. Same thing happened the next day. Swapped the boot to see if that was bad still was in 4 the next day. Checked the spark plug the next day for moisture and nothing so we don't think the head gasket is bad also oil is fine not milky and coolint is fine also. There is 86k on the car. Any suggestions on what it could be from here? Thank you in advance.