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Thread: Low idle on V8

  1. #1
    Join Date
    Aug 2009
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    Low idle on V8

    When I come to a stop my V8 idles low and lumpy, WTF? But when I put the heater fans on it returns to normal??

  2. #2
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    Only when the engine is cold, or even when it's heated up properly?
    Have you checked for blocked manifold water hoses?

    Have you checked the stepper motor?

  3. #3
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    Only does this when warm, what manifold waterhoses?
    Cleaned stepper motor already.

  4. #4
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    Perth
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    the heater or air cond, it will rev up with a/c on mine used to do this i fixed it with new motor

  5. #5
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    When I have the heater on

  6. #6
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    As far as I know, even the 3.9 V8 should have SOME type of water bypass to the inlet manifold, otherwise your incoming air can be too cold and you will get poor vaporisation and fuel/air mix.

    While I'm thinking of that: maybe issues with the air temp sensor?

  7. #7
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    When I come to a stop my V8 idles low and lumpy, WTF? But when I put the heater fans on it returns to normal??
    On a Thor I would be looking at plugs /leads/coils.
    The IAC on a Thor is very powerful and should be able to compensate for minor problems. Maybe it is dirty although it is a sliding valve arrangement not a plunger like the old 3.9.
    Maybe the reason it goes better with the heater fan is that the IAC compensates for the extra electrical load and the denser mixture just makes a bad plug fire. Otherwise there is AFAIK no connection.

    Just another couple of thoughts, crank position sensor and cam position sensor( although AFAIK the cam sensor is only used at startup to ID the cylinders to the ECU)
    In any case the first thing to do is maybe have a code read.
    Regards Philip A

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