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Rough Idle After Batt Disconnect (ECM Full Reset)

Discussion in 'Engine' started by navylife59, Feb 24, 2008.

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  1. navylife59

    navylife59 Super Moderator Staff Member

    Mar 22, 2006
    Emory, Texas or Gretna, LA
    This might be a possible cause for rough idle after a full ECM reset aka batt disconnect. This should only be temporary. Understanding how this works can prevent possible issues and misunderstandings in the future.

    The ECM monitors the intake air amount during idling and the ignition timing. When the Engine Coolant Temperature (ECT) is between -10°C and 50°C (14°F and 122°F), the ECM calculates the idling intake air amount for 10 seconds, beginning 3 seconds after the engine starts. When the accumulated value is below the threshold, the ECM interprets this as a malfunction in the Idle Speed Control (ISC) system at cold start. The ECM also monitors the ignition timing at cold start, and judges it to be incorrect when it is advanced to the same value for a warm engine for 5 seconds or more of the 10 second monitoring period.

    P050A is detected when all conditions below are met (2 trip detection logic).
    1. The ECT is between -10°C and 50°C (14°F and 122°F) when the engine starts.
    2. The engine idles for 13 seconds after engine start.
    3. The accumulated intake air amount is below the threshold. The ECM sets the DTC and illuminates the MIL 13 seconds after the engine is next started.

    When the negative battery terminal is disconnected during inspection or repairs, the ISC learning values are cleared. The ISC learning must be performed by warming up the engine and idling for 5 minutes with the ECT at 75°C (167°F) or more because DTCs cannot be detected with the ISC learning values cleared.
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