rough idle on 2002 Cadillac DeVille

4.6 noth star i change the plugs and wires crank sensors fuel filter code PO300 mutiple mis fire what else could this be

2 answers
Here is a ton of great information about the P0300 code: http://repairpal.com/OBD-Code-P0300
Try the Vacuum Hose's or Brake Booster.