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
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running throughthe trouble shooting steps it says the most likely suspect would be the"down stream" oxygen sensor , now this is where I'm confused , would downstream be after the converter ?Thanks Jose