Question about 1996 Volkswagen Jetta

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My 1996 Jetta 2.0L failed emissions. The CO was too high. Is there an air/fuel mixture adjustment anywhere? I changed the oil and checked the air filter, but couldn't find any way to adjust the air/fuel mixture.

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  • yadayada
    yadayada Aug 26, 2010

    there is no such adjustment

  • aldo_hoyt Aug 26, 2010

    I suspected there was no adjustment. I dug out my old VAG tester and found out that the #1 O2 sensor was bad.

  • aldo_hoyt Aug 26, 2010

    I suspected as much.

  • aldo_hoyt Aug 26, 2010

    My OBDII tester reported that the O2 sensor voltage was low, but the VAG tester specifically stated that the O2 sensor was bad.



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First off do you know when the CO was too high? was it at idle or accelerating? The mass air flow sensor adjusted the mixture based off of readings. I would take it all apart and clean everything. Also your front o2 sensor may need to be replaced as well.

1) take the intake hose off of the throttle body, and air mass meter. Clean this completely with carburetor cleaner.
2) remove mass air meter from air filter housing, and clean this also
3) clean throttle body completely with carb cleaner and a soft brush
4) check integrity of the entire PCV system from where it clips onto the box on the front of the engine block, up through the diaphragm on the valve cover and the hose leading to the intake tract. All are likely in need of replacement.
Thank you,

Posted on Aug 26, 2010


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