rough idle

I got a 2001 XJ with 50,000 miles on it...I recently changed the plugs on it and set to right gap and the air filter is new..As teh engine gets warmer the idle gets rougher sometimes and i get a rattle on the right rear side ..Is it possible the catalytic converter could have came loose...Any help or opinions would be helpful...Thanks

You "could" have a loose CAT, as the engine gets warmer, do you notice if the CAT starts to glow, or get noticably hotter than normal. I have an 00 XJ with 99K+, never had an issue with the CAT. What kind of plugs did you install. If they were a Platnum plug, they should have been pre-gapped. I have the Bosch Platnum plugs in mine never had any problems.

I did have the platniums in it and i just put them in again and did check the gap..Now that i think about it sometimes before or after bumps the noise stops...Im probably gonna change the cat anyways

Depending on the cost, you might want to look into Random Technologies, high flow CAT.