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Possible Vacuum Leak

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    Possible Vacuum Leak

    Hello all,
    I drive a 1986 BMW 325es. It hasn't given me any problems for about 10,000 miles until just the other day. I started the car up and my RPMs kept climbing until they were at about 2500. If I drive the car around, the idle speed will increase to about 3000. I'm fairly certain it's a vacuum leak, but I have no idea how to diagnose where the leak is. I have already cleaned my TPS and ICV, and I don't think they're the root of the problem. If anyone has any advice, please help.

    #2
    Any time I have a vacuum leak it makes my idle low and rough.

    Check your oil fill cap and dipstick seals.
    After your engine is warm maybe unplug the cold start injector in case it's firing.

    When the idle control is unplugged the engine is supposed to idle at 2000, so you could have a dead icv.

    Throttle position sensor needs to be checked, make sure idle switch is working and full throttle switch is working.

    You have a Bentley manual? There's lots of things to test and check, fuel system, intake/air system, and ignition.

    Play with the throttle with the hood up, if you're lucky it's just a sticky throttle cable.
    My son has the 1987 325e, 2 door, 5speed
    I daily the 1989 325i, 4 door, 5speed

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      #3
      Search smoke test here or on Google. You'll find plenty of information including DIY on making smoke machine.

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        #4
        I'm inclined to think vacuum leak because I can hold my hand over the intake and it'll drop to about 1000 RPM, but not get choked out. My throttle cable is fine unfortunately. My throttle can be completely shut but my engine will still be revving at close to 3000 rpm.

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          #5
          Originally posted by dnguyen1963 View Post
          Search smoke test here or on Google. You'll find plenty of information including DIY on making smoke machine.
          Only way to really search out leaks.


          And do not rule out the throttle cable. They are old, crusty things by this time. Perhaps snagged, kinked, stuck in place...
          ACS S3 Build / Dinan 5 E34

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            #6
            massive vacuum leak wow. check the hose going from the valve cover vent, under the intake and into the throttle body.

            if the throttle plate is shut and it does this then I would take a close look at the injector seals as well as the intake manifold gaskets.

            good luck! just pull the intake and replace it all if you car about the car. intake boot, intake manifold gaskets, breather hose, and injector orings (just send the injectors to MEPEH on the forum here for a $40 rebuild) - you can do this job right for under $150 in parts.

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              #7
              With the age of the cars, when issues like this arise, I agree w/ you 5toes... get in there, fix the many possible problems if ya can.
              ACS S3 Build / Dinan 5 E34

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