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Car Shakes Under Cold Start after 1 week of sitting

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    Car Shakes Under Cold Start after 1 week of sitting

    Hello All!

    So I've had my 91 318ic for about 2 months now. I'd noticed under cold starts my RPM dips to about 500 rpm for about 1/2 a second and then jumps right back up to around 1,000rpm. Once the cars warm it'll sit where it should (750 - 800rpm). This was something I was gonna look into once I have the car up on blocks in a month (I have new interior, gauge cluster, oil change, steering fluid change, and a few other small line items coming in) I've been driving the car almost every day and that little dip in the RPMs at coldstart was the only thing I've noticed. However last week I went back to my parent's house for a week and left my car at my house.

    I come to start it today and it starts shaking violently. While the car was shaking, the RPMs were dipping and I had to throttle it a few times to keep the car from dying. After about 20 seconds the car slowly started to shake less until it was idling smoothly again (about a minute). Once idling smoothly, it stopped shaking completely. I didn't notice anything once the car was warm and on the road. Does anyone know what this could be? I've read through some "car shaking" threads and haven't been able to find one with the same issue. Thanks in advance!

    #2
    It sounds like a gunked-up idle control valve. As the engine warms up, the oil residue softens and allows the idle control valve vane to more more freely. The ICV is buried on the back of the engine against the firewall, sort of under the main plenum of the upper intake manifold. It is only held on by the 2 hoses connected to it, and the little bracket that is held down by the rear-most intake manifold bolt. Removal is fairly simple.

    To clean it, take it off and keep the hose barbs downward. Spray some carb cleaner through both sides. If you shake it (or more like violently rotate it along its axis) you should hear a little metallic clanging which will indicate that the vane is moving freely. You may need to shoot it out a few times. Just try to keep it facing down so that the carb cleaner does not drain into the main body too much. It is quite unlikely to harm anything, but it is still good to keep solvents where they belong.

    If you happen to have access to a 12V power supply, you can try applying 12V to the terminals intermittently to see the little vane move. That is a slightly more reliable test than shaking it lol.

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      #3
      Thanks for the advice! Planning on cleaning the ICV this weekend!

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