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Rough idle after battery disconnected

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  • 25-01-2008 10:55pm
    #1
    Rebeller
    Closed Accounts Posts: 271 ✭✭


    Hi,

    1999 Hyundai accent. I disconnected the battery negative terminal for around 5 minutes. After reconnection the car has now begun to idle roughly. It's starts without a problem and there is no loss of power at high speeds but whenever I have to stop at lights etc.the engine idle speed seems to drop momentarily (with the headlamps dimming for a split second) and then increase. I never had this problem prior to disconnecting and reconnecting the battery.

    Is there any way I could have damaged the alternator?

    All suggestions welcome:confused:


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    #2
    Oilrig
    Closed Accounts Posts: 727 ✭✭✭Oilrig


    Disconnecting either (same effect) battery lead while the engine is running is usually the quickest way to kill your alternator. Disconnecting the lead causes a voltage spike - usually around 300V, the voltage regulator in the alternator is normally the victim.

    If it has been fried, I'd be inclined to look for a second hand one at a scrappy, repair parts for Hyundai alternators are a bit hit & miss.


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    #3
    Spunj
    Registered Users Posts: 437 ✭✭Spunj


    More than likely the ECU has just lost its timing settings. It can take a while for it to relearn them.

    As far as I recall some manufacturers recommend a few minutes at 1500-2000 rpm followed by a drive where you go up and down the rev range a bit like a B road type drive of 10 miles or so.


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    #4
    Rebeller
    Closed Accounts Posts: 271 ✭✭Rebeller


    Oilrig wrote: »
    Disconnecting either (same effect) battery lead while the engine is running is usually the quickest way to kill your alternator.

    The engine was off when battery was disconnected but thanks anyway.
    Spunj wrote:
    More than likely the ECU has just lost its timing settings. It can take a while for it to relearn them.

    This sounds more likely since rpms were fine at idle prior to disconnecting the battery.
    Spunj wrote:
    As far as I recall some manufacturers recommend a few minutes at 1500-2000 rpm followed by a drive where you go up and down the rev range a bit like a B road type drive of 10 miles or so.

    I'll give it a go. Thanks


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