Hey Folks, I have an 09 Mariner that will just not keep the 0304 and 0430 engine codes from clearing. I have changed the following:
Plugs
Coils
Wires
Injectors
O2 sensors Both banks both sensors
Cam Sensor Bank 2
I have performed the following maintenance:
Intake Plenum removal (several times)
EGR valve tubes cleaned
Upper Lube with premium Engine Lube
Seafoam the intake several times.

Here's the underwear twister! I cannot seem to locate the reasons for the cylinder misfire, or the Cat Efficiency out of range, My mechanic who is VERY good has come to his wits end trying to diagnose this cluster! Here is a snapshot of the last engine code thrown. It was both the 0304 and 0430 codes at once:

Calculated engine load: 83.1 %
Engine coolant temperature: 210.2 F
Short term fuel trim—Bank 1: 2.34 %
Long term fuel trim—Bank 1: -1.56 %
Short term fuel trim—Bank 2: 7.81 %
Long term fuel trim—Bank 2: 4.69 %
Intake manifold absolute pressure: 80 kPa
Engine RPM: 2515.5 rpm
Vehicle speed: 11.18 mph
Timing advance: 31.0 degrees
Intake air temperature: 96.8 F
MAF air flow rate: 41.86 g/s
Throttle position: 27.5 %
Oxygen Sensor 1 Voltage: 0.35 V
Oxygen Sensor 1 Short term fuel trim: 1.56 %
Oxygen Sensor 5 Voltage: 0.63 V
Oxygen Sensor 5 Short term fuel trim: 7.81 %
Run time since engine start: 72 s
Commanded EGR: 0.0 %
Commanded evaporative purge: 16.9 %
Fuel Tank Level Input: 54.9 %
Warm-ups since codes cleared: 3
Distance traveled since codes cleared: 13.04 mi
Evap. System Vapor Pressure: 34.0 Pa
Absolute Barometric Pressure: 98 kPa
Catalyst Temperature: Bank 1, Sensor 1: 986.0 F
Catalyst Temperature: Bank 2, Sensor 1: 986.0 F
Control module voltage: 13.84 V
Absolute load value: 57.25 %
Fuel–Air commanded equivalence ratio: 12850.2
Relative throttle position: 15.69 %
Ambient air temperature: 73.4 F
Absolute throttle position B: 43.92 %
Accelerator pedal position D: 32.55 %
Accelerator pedal position E: 16.47 %
Commanded throttle actuator: 25.1 %

The last thing to look at IMO might be the computer. Any help/comments/questions/suggestions it would be GREATLY appreciated!