Nissan Repair: Knock Sensor, advance auto parts, catalytic convertor

Question
I have a 1999 Nissan Frontier 4x4 automatic with a v-6 engine.  The service engine light will come on for awhile and then go off only to come back on later, maybe a day, sometimes more.  It will also misfire at time worse than others, however, seems to only misfire when at an idle, runs very good under some acceleration.
Advance auto parts checked for a code and told me the code said knock sensor and something about the catalytic convertor, I am not sure the exact words.
Can you give me some idea of what may be going on?
Thanks

Answer
Billy,

Replace the converter and that will get rid of that code and replace the knock sensor.  The knock sensor can be obtained from the parts store and it is a difficult job replacing it since it is under the intake.  Once the converter and knock sensor are replaced clear the codes by disconnecting the battery for five minutes and reconnecting it.