S320 - foul smell bad CAT?
 

I was recently following my S320 in traffic (wife was driving...) and noticed a pesty foul exhaust smell.
Now I have had some problems with a surging idle and some ruff running at the highway. And a Oxygen sensor warning (check engine light)
Is it possible my Catalyst is bad or clogged?
How would I check?
regards,
Sab.

If you never changed your oxygen sensor ( with 166 k miles ), now would be a good time to do it. ;)
Many times a bad smelling cat. converter indicates rich fuel mixtures ( could be caused by a worn out oxygen sensor ).
How is your fuel consumption & did you ever investigate the Check Engine light ?
If your converter was plugged, you would know it ( no power from the engine ).

If it smells like rotten eggs it is your cats, they may be clogged causing poor exhaust and partial , soon to be full, loss of power or partially clogged and burned out causing poor ecu/ 02 sensor readings. Or your 02 sensor(s) is bad cauing the engine to run overly rich and is killing the cats , chicken or the egg, egg or the chicken. It is hard to test an 02 sensor. Find out soon as the overly rich engine can cause carbon build-up

Thanks guys,
I just recently replaced the O2 sensors and the error came back and I noticed the foul (rotten egg) smell. I am not sure if it smelled like that before I changed the sensors, it probably did.
So as I understand it may be the cats. But how can I test?
regards,
Sab.

Not trying to be smart but double check your work. Check the conections and also make sure that the wires are not hanging down and have burned through from contact with the exhaust pipe. Checking the cats requires emissions testing I think. You can have the cats cut out and new ones welded in. Summit racing sells the ones for my old range rover -try them.. If you have them welded in make sure the welder does not get any weld in the bung hole / receiver hole for the O2's ( so they will go back in when he is done)

Could you elaborate on this a little more?
I still think you are running way too rich.

Manny,
The car started to develop a slight loss of power at times. For example, when cruising at 80 mph steady, I could feel it hesitate just slightly (100 rpm drop). It also started to have a surging idle at times (intermittend up and down between 600 and 1000). Somwhere along the line the check engine light came on. And it now really hesitates on take off.
I had it read out and it indicated O2 sensor malfunction.
I bought both sensors and replaced them and reset the check engine light. The symptoms are the same after the new sensors and the light came right back on. I don't know if it is the same error code.
I checked the sensors and they are connected properly.
So my thoughts are cats or vacuum leak, but I am by no means an expert.
I apreciate everyones help,
Thanks,
Sab.