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    inconsistent Idle

    Hey all:

    My b25 sometimes idles at like 950 rpm (getting close to 1000). I notice that it does this when it's worm more often when it's cold.
    For example: I'll turn the car on and it sits pretty smoothly at 750, but when I put it in neutral at a stoplight after some driving, it'll be at like 950.

    One interesting thing to note is that the car runs cool according to the temp gauge on the dash (runs slightly above the left tick and will creep up ever so slightly when stopped or under heavy load). All this despite having an 80c thermostat in there. I'm not sure if this would have any bearing, but I figured the more info the better.

    Is this a quirk that I shouldn't worry about? or something that merits more investigation and potential action?
    '91 325i


    #2
    Erratic or high idle is often due to vacuum leaks. Your temp raises when stopping the car is most likely due to a bad fan clutch.

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      #3
      +1 on intake leaks being a likely cause of the idle problem. A smoke test will find them.

      The behavior of the temperature gauge is normal and correct. It may be reading slightly low, but with an 80C thermostat the normal position should be in between the 1st mark and the 12 o'clock mark. It is normal in warmer weather to see the needle rise slightly when idling or under heavy load.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL

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        #4
        Originally posted by jlevie View Post
        +1 on intake leaks being a likely cause of the idle problem. A smoke test will find them.

        The behavior of the temperature gauge is normal and correct. It may be reading slightly low, but with an 80C thermostat the normal position should be in between the 1st mark and the 12 o'clock mark. It is normal in warmer weather to see the needle rise slightly when idling or under heavy load.
        Okay cool thanks: I did just replace the fan clutch, too.

        But wouldn't a vacuum leak make me idle high all the time? Sometimes the idle is right where it should be and reasonably smooth and other times it is higher. Maybe is it because a leaky valve opens or closes?
        '91 325i

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          #5
          Check the elbows going into the throttle body. They are often the cause for vacuum leaks when the engine is warm/hot.

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            #6
            Ok thank you, I will!
            '91 325i

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