Hello, I have a 01' Hyundai Elantra and been having issues with it idling rough at stops and stalls out at stops every once in a while..

The issue has been going on for about a year and a half and seems to be getting worse. The check engine light came on and reads "downstream oxygen sensor slow to respond" so I bought both new upstream and downstream O2 sensors and replaced them both out.. didn't fix the problem and check engine light came on again giving the same read out.. i replaced out the downstream O2 sensor again (since under warranty) just in case it was faulty and it still gives the same error.

I have also already replaced plugs and filters..

Does anyone have any insight? Could it be a clogged catalytic converter causing the reading for a bad sensor?

any help is great.

 

You got codes... post the exact codes...

Look for cracked exhaust manifold, need to look from under neath at the legs from head into the point where it all dumps into the top of the cat, remove the shield and look there too..

Have dealer run VIN on WEBDCS for open "VO4" exhaust manifold recall.

With the car stone cold, open hood, have assistant start engine, do you hear and smell exhaust leak noise/smell exhaust fumes between manifold and radiator area ??

Front exhaust pipe leak at the accordion/flex section ??

Repair leaks as required to keep from goofing sensor values back to PCM.

Misfire codes ?? intake gasket is common vacuum leak/rough idle/misfire point, can of carb and spritz along seam where intake meets head.