Car care advice

Why Is My Engine Stalling After Replacing the Battery?

It is not uncommon for late model vehicles to stall after the battery has gone dead or has been disconnected.

The engine computer has a basic idle speed control setting for when the engine is new. As you drive the car, deposits build up on the throttle body, which restricts the air flow and reduces the idle speed. The engine control computer compensates for this by opening the idle air bypass valve to achieve the correct idle speed. The computer stores this new bypass valve position in its memory. Over time, this can become a fairly substantial adjustment, but the change occurs so gradually, you will never notice it happening.

Unfortunately, when the battery is disconnected, some late model vehicles will lose this learned idle position, which will cause the vehicle to stall.

You can try one or both of these procedures try to correct this problem:

Clean the deposits built up on the throttle body (Throttle Body Service) using aerosol brake cleaner and a shop towel. This will allow the default idle air bypass valve value to function correctly. The idle learn procedure will begin again as it did when the vehicle was new. Some basic repair knowledge may be necessary to complete this procedure.

You can also perform the following procedure to try to force the engine computer to quickly relearn the necessary bypass valve position.

  1. Warm the engine, but hold your foot on the throttle as necessary to keep the engine running.
  2. With the transmission in Park, slowly release the throttle so that the engine will idle on its own. You may have to work at this a bit.
  3. Let the engine idle on its own for about one minute.
  4. Continue to let the engine idle and with your foot on the brake, place the transmission in Drive and let the engine idle for another minute.
  5. Continue to let the engine idle with your foot on the brake and the transmission in Drive. Turn the A/C on and let the engine idle for another minute with the A/C compressor running.
  6. Turn the ignition off and wait a minute.

If this corrects your problem—great! If not, you may need the help of your local service technician.

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