oxygen sensor elantra

[Strike_one]

Hi
I have a 96 Elantra that is idling very rough and has un-usually high gas
consumption.
I've brought the car into a dealer and , they tell me that both oxygen
sensors need to be replaced it pointed out P1 and P2 sensors and the MAS
( mass air flow sensor).
The MAS sensor was replaced and the car is now driveable
I suspect only one O2 is faulty I'd hate to change both at $200 cnd each.
On the Hyundai tech site http://www.hmaservice.com/webtech/ running through
the trouble shooting steps it says the most likely suspect would be the
"down stream" oxygen sensor , now this is where I'm confused , would down
stream be after the converter ?
Thanks
Jose

 

[Jody]

yes, down streams after the cat,, id replace both at that cars age

 

[hyundaitech]

The downstream oxygen sensor won't affect your fuel mileage. The computer
uses it to assess the efficiency of the converter.