Ok, are the codes you posted the only codes you are getting? If so the codes mean.
P0301 - Misfire in cylinder #1
P0304 - Misfire in cylinder #4
FYI - The codes P0301 - P0306 are misfire codes for each cylinder
P0300 - Random or Multiple cylinder misfire.
Now causes for these codes are.
Weak Fuel Pump and/or Fuel Pressure Regulator
Bad Plug Wires
dirty, clogged or inoperative fuel injector
Low cylinder compression
Leaky EGR Valve
Blown Head gasket
Thursday, June 3rd, 2010 AT 8:20 AM