Timing chain worn???

My car has recently begun to run like crap.
It started around the time that my o2 sensor blew out of the cat. I've since replaced both 02 sensors and an idl;e pulley but it still runs crappy
S/S very rough idle, I usually have to throw it in n,and stumbling on acceleration till cruising speed. My mechanic, not licensed, says it might be the timing chain tensioners, but I was hoping otherwise because that is about a 750$ job. a code 0304 knock sensor comes up but he says it means nothing also ive checke the fuel filter, spark plugs, cap and rotor and they are all fine
has anyone had this problem before and what is your advice?
thanks

INFO PLEASE. Year/miles.

It's a 95 altima gxe/le, 2.4 L, with about 147,000 miles

did you replace your cat?

a bad knock sensor can cause the car to run poorly because it cant adjust the timing without it also. Check your egr valve and clean it out and then re-install it.
the timing chains really dont wear out. The only things that rarely wears out is the bracket on top between the cams on top. I removed mine.