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Occasional 200 rpm swing at idle from 600-800

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    Occasional 200 rpm swing at idle from 600-800

    I have a very low mileage (29k) 90 E30 that will sometime at idle bounce between 600 and 800 rpm. Goosing the throttle will usually stop it for a time. I just replaced plugs and air filter, no obvious leaks, or cracked boot. Also no codes or lights.

    The biggest mystery is that it comes and goes. Drives fine otherwise.

    Could it be a dirty ICV? I guess I will clean that next.

    #2
    No help at all??

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      #3
      Did you clean the ICV

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        #4
        I pulled the icv, nothing obvious inside , but I cleaned anyway and remounted. Car started and drove fine, steady idle. I hope that is it, but I have had steady idles before and then the surging comes back.

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          #5
          Sounds like ICV, but also could be failing FPR or fuel pump. Even through the mileage is low, it is Florida and parts do go bad over time.

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            #6
            More often than not, surging idle is related to small vacuum leak somewhere. Perform a smoke test to rule out vacuum leak before looking at other items.

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