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The most common fail item associated with the P1131 is going to be a faulty Oxygen Sensor (Bank1 Sensor1). Check the Air Filter to make sure it is not excessively dirty. Check the Air Filter housing for any signs of blockage (leaves, trash, etc). Check that there are no intake air leaks. Check for any broken, disconnected or holes in vacuum lines. If this all checks ok, suspect a faulty Oxygen Sensor.