Russ,
I know the list that on this forum says something about the "driver" for your P1684 code, but on other Code Lists the P1684 is nothing to worry about. Even if you've never touched the battery, you can still get this code.
1684 =The battery has been disconnected within the last 50 starts.
P303 is a misfire in Cylinder #3 and yes, it could mean you need new plugs or wires.
Oh Yea, WELCOME to the forum.
