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My 2005 Mazda 6 4 cylinder has a rough idle and the engine light is on, it was throwing an o2 front sensor code so I replaced it and it still showing an o2 code and can't figure it out. any help would be grateful.
 

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Have you started with the basics? Air filter/maf/throttle body cleaning. Spark plug check. Spark wire check. Ignition coils. Vacuum leak.


I don't have a 2005 so I don't know if every single thing like the ignition coils will apply, but those are usually a good bet it will be one of those if you've already fixed the code. I assume you have unplugged the battery for an amount of time and plugged it back in also after the o2 change?
 

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Just had the same problem with my 2009 Mazda 6, 3.7L. After checking all the air/emissions stuff that I could, I gave up and took it to the dealer. They found a crack in the upper air intake manifold which is plastic.
 

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Rough idle is common if there is an intake vacuum leak. If you have an engine code then that is the first place to go. A faulty oxygen sensor 1 (either bank 1 or bank 2) is the sensor that controls the fuel mixture and will absolutely cause rough idle. Sensor 2 (after the catalyst) only tells the engine if the catalytic converter is operating correctly.
The most common place for vacuum leak is the intake air tube (accordion tube). After that it is likely one of the tubes that plug into the intake manifold.
 

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Dumb question, but do you have to clear the code manually after replacing the sensor?
 
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