DTC P0300-P0304: CYLINDER OR MULTIPLE CYLINDER MISFIRE
Misfire is detected when crankshaft position sensor detects a fluctuation in engine speed. Possible causes are:
Incorrect spark plugs.Insufficient compression.Incorrect fuel pressure.Defective EGR valve.Injector circuit open or shorted.Defective injectors.Intake air leak.Secondary ignition circuit open or shorted.Lack of fuel.Defective drive plate or flywheel.Defective front HO2S.Incorrect distributor rotor.
If the symptoms are rough idle or miss at idle but runs good off idle, check the intake gasket for a leak, spray a little carb cleaner near #4 intake runner and cylinder head, if the idle smooths out you've got an intake leak.
HO2S = Heated Oxygen Sensor = commonly called O2 sensor.
Depends on the leakage. If it is due to a bad gasket caused by unloosensed nuts, a gasket replacement is required.
If the leakage is minor, gasket sealants of the paste type would be sufficient. Most of these sealants can be purchased at your local parts outles.