Recently my xj sat for a couple weeks and today when started my idle very low and exhaust smell is unbarable. Cat is discolored and smoking around pipe. Has anyone seen this before?

 

If it smells like rotten eggs its bad and if it gets nice and red its deffinetly bad. Id replace it and go from their

 

Id say u got a plugged cat id pull the exhaust and replace it. Pretty easy job. You could easily have a rats nest in your exhaust tho if it sat for a bit. And if i were u id look for an hi flow replacement

 

Will do that. Thanks

 

Cats don't go "bad" from sitting 2 weeks.

Check for a misfire - the unburned fuel from that misfiring cylinder is burning in the cat, making the smell and discoloration.
Smell from a cat converter means it's getting overloaded with HC.

 

X2. If everything is working properly the cat should never go bad. When the "check engine" light comes on it is telling you there is a problem and you should fix it fast before the catalytic converter is damaged. The check engine light is there to save the catalytic converter.

 

Ok but what if no check engine light??

 

Also check for moisture in the distributer cap

 

Turned out to be a vacuum hose leak.. Going into the map sensor.