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A/C kills my idle....any suggestions 700 1991

posted by  The Plastic Lizard on  Wed Aug 20 01:57 CST 2003
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last visit: Tue Nov 8 09:34 CST 2011
[RELATED]

On my 91 740, I've done most of the P.M. work as described in the FAQs to get a smooth idle. It now idles right at 750 when in gear with my foot on the brake. However, when the AC compressor kicks in the idle drops to about 500 rpms and the entire car shimmys and shakes, making the most God awful rattle.

Is there a reason that the computer or IAC doesn't compensate for this by raising the idle back up? What should I check next.

Thanks
TPL







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    A/C kills my idle....any suggestions 700 1991

    posted by  david hunter on  Sat Aug 23 05:44 CST 2003
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    last visit: Mon Jun 30 22:10 CST 2014
    [RELATED]

    The idle speed on your car is not adjustble, Its is controlled by the IAC. Not even sure if the 91 has a base idle adjustment (the black Knob on throttle body). How did you set up the idle ? What is idle speed in nuetral?
    --
    David Hunter








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    A/C kills my idle....any suggestions 700 1991

    posted by  ivan on  Wed Aug 20 11:01 CST 2003
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    last visit: Wed Aug 22 20:55 CST 2012
    [RELATED]

    Your A/C comprossor is almost dead,
    or you have way too much refrigerant.







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      A/C kills my idle....any suggestions 700 1991

      posted by  The Plastic Lizard on  Thu Aug 21 07:33 CST 2003
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      last visit: Tue Nov 8 09:34 CST 2011
      [RELATED]

      Since I haven't put any additional coolant in during the past 7 years, I know that can't be it. Why would you think the compressor is dieing? And even if it was, why whouldn't the computer compensate for the additional power drain?

      Thanks








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    A/C kills my idle....any suggestions 700 1991

    posted by  Steve on  Wed Aug 20 06:47 CST 2003
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    last visit: Fri Oct 24 07:16 CST 2014
    [RELATED]

    When the compressor is on, the ECU compensates for increased engine load by operating the IAC to maintain the same 750 rpm or so by openning slightly more. Take a look at your wiring connections between the compressor and the ECU.







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