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AutoMD ... 8/16/2010
1988 BMW 325 Base 6Cyl2.7L - Engine
why does my car get arrattic idle
1 Answer
  • Ladiesman217
    Ladiesman217 8/17/2010
    Check the voltage on your Throttle Position sensor using a voltmeter

    Unplug your Idle Air Control Valve (IAC), which is located on the back of the intake manifold. Doing this SHOULD cause the idle speed to increase if it functioning properly. If it does not increase, then you have found your problem... go get a new one. If the idle speed does increase, begin to turn the bypass screw on the throttle body and bring the idle of the car down to like 500-600 rpm, then plug back in your IAC valve. This should bring the speed back to a normal 800 or so rpm. In the event that doesn't work...

    Check your ignition timing

    Chances are now that you have a vacuum leak somewhere. Trace all of the vacuum lines and make sure there is no leak anywhere. Some people use a little bit of lubricant and spray it on the hoses to watch for bubbles.

    Another thing that sometimes causes cars to idle poorly is too much fuel. Do you have a Fuel Pressure regulator? Make sure that it has a vacuum reference and that it is within specs at static idle.

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