The tune-up would be a great start. While you're checking your plugs, consider replacing the distributor cap & rotor. If you have any hairline crack in the cap, you will end up with moisture inside of the distributor, which will affect the timing. Corrosion on the contacts will delay the spark from actually reaching the plugs, giving you a misfire. My pickup truck was doing this for a while, and I just did the tune-up that it so desperately needed and its running like a champ. Things to check, (and likely replace if its been a while):
- Distributor Cap AND Rotor, (if you replace one, its good practice to replace both).
I was getting a similar engine code for the O2 sensor on the truck, and that has since gone away. It was sporadically turning on, especially when it was moist outside - thanks to that hairline crack in the distributor cap. Funny how so many problems and symptoms can arise from one simple problem.
Hope that helps.