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rough idle and oxygen sensor (need some readings off someone else to compare) 200 1984

posted by  med1963 on  Fri Oct 17 14:29 CST 2008
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last visit: Fri Sep 11 05:50 CST 2009
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had a rough idle problem. checked everything, and in the end just took the oxygen sensor line and shorted it to ground, and idle seemed to even out (still not the best, but it runs a lot better). when i measured the milli Volts coming off the sensor, at idle it was about 130 mV and with engine revved up, it went to about 350 mV. anyone else take readings off the oxygen sensor so i can compare

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    rough idle and oxygen sensor (need some readings off someone else to compare) 200 1984

    posted by  runwld2 on  Fri Oct 17 16:09 CST 2008
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    last visit: Tue Sep 30 13:11 CST 2014
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    The nominal value for the O2 sensor is 0.5 volts, and with a modern digital VOM you should see the voltage oscillate from about 0.2 to 0.8 volts on the meter, at idle. At higher revs, it will oscillate faster. Your readings are all low, indicating a lean mixture. Which lead did you short to ground, the one to the ECU?,that will tell the ECU the engine is VERY lean, and it will richen the mix. If the idle smooths, it may mean you were too lean before.
    Everything points to a lean mixture, which usually means an air leak. Check every hose.....but what I found on my 84 was the intake gasket was broken. Car also had high NOx emissions, and eventually was impossible to start below freezing (too lean).
    Oh, but of course your O2 sensor could be bad. If it is old, that may be the place to start. It is pretty difficult to test a sensor.
    --
    84 242Ti IPD bars&springs, 89 745 16v M46 IPD bars, 89 744 16v M46 IPD bars, 90 745 AW70, 91 245SE AW70 IPD bars, 93 245 CLassic M47







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