P0171 is a vacuum leak, if that BBV has a tear/crack in it, it could cause the code.

A P0300 only being covered under a lubrication parts of a warranty???

What kinda crap is that, a misfire has nothing to do with what gets oiled in a motor and what doesnt. The misfire is almost always ignition related like I said, so plugs, wires, coil packs etc etc.

I would remove to champion plugs and put AC delco plugs in it though, champion's are a more of a chrysler product thing.