I have a 95 4runner with a 3.4 in it. Tha cat smells on warm up, is it bad or one or both of the O2 sensors? If I relace the 02 sensor shopuld I do both? No one carries the rear sensor in stock so it seams like they are not offten replaced. Also, my cat does not rattle.
Thanks

 

cat could be plugged

 

I wouldn't base 02 sensor replacement on smell. There are too many variables. Plus, the rear 02 sensor rarely goes out; it's usually the pre-cat sensor that takes a dump.

BTW, what do you mean the cat smells? You mean the exhaust, right? Can you describe the smell? Is it a raw unburnt fuel smell, or a rotten egg smell?

Have you been tracking your mpg?

 

If you're not throwing a CEL, then I'd try changing your brand of gas first. I doubt it's the O2 sensors so I would guess it's either the gas or the converter (OR it's a normal odor that you've just noticed).