I can get anew O2 sensor for 30 u.s , and since i am putting a rb header on, i figured i would replace. do they get old, wear out, inaccurate?? my car has 270,000kms idles rough but everything else is good. is it a good idea? thanks

 

What year is the car?

 

84 gsl-se 13b efi

 

It can hurt gas mileage, which may cripple performance, but not likely. I would replace it if you are doing the exhaust, but I wouldn't replace it for performance gains. To make it idle smoother, maybe you need: new plugs, rotor, cap, wires, clean fuel injectors/replace. Being a 12A owner, I'm not that familiar with all the little "tricks" you can do to the 13B, but those suggestions are some basic things you might want to check out.

 

Solving GSL-SE idle problems

http://mrmazda.members.atlantic.net/gslseidle.html

Also, get a shop manual.

http://www.monmouth.com/%7Erothe/shop_manuals.html