why does my honda civic idle up and down?

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  • 1 decade ago
    Favorite Answer

    there are three usual causes. The engine idle is controlled by an "idle air control valve" or IACV. That valve is an electrical motor that moves a plunger into and out of a passage in the throttle body that allows air to bypass the throttle plates and thereby maintain a target idle speed.

    the first thing that happens is that carbon (think of soot in a chimney) coats the inside of the air bypass passage and restrits the amount of air that can flow through it. when that happens, the engine starts 'gasping' for air and pulls the throttle plates open and closed as it tries to run.

    the second thing is that the carbon will gum up the plunger on the IACV so that it doesn't move freely in and out of the passage to regulate the idle. when it moves spastically, the engine speed jumps up and down.

    a third possibility is that the IACV is electrically dead and that means there is no control of the idle speed and the engine 'hunts' for an idle.

    there is the possibility of a vacuum leak causing the problem, but in perspective with the top three causes, that possibility is remote at best.

    The solutions are to clean the throttle body with an aerosol spray throttle body or carburetor cleaner and spray into the port on the inside wall of the venturi on the air filter side. that is the bypass port. be sure to clean the entire venturi while your there by spraying around the throttle plate (the "butterfly")and the throttle plate itself.

    if that doesn't resolve the condtion, the IACV will have to be removed and cleaned. if that doesn't work, then you need to replace the IACV,

    hope that helps

  • heckel
    Lv 4
    4 years ago

    Engine Idles Up And Down

  • 1 decade ago

    i have run in to this problem before and i checked everything changes spark plugs and wires rotor button even checked the hoses ..and it turned out to be a vac. hose and i replaced that and it quit doing it so check all the above

  • ?
    Lv 7
    1 decade ago

    ...timing issue!!!???!!!

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