What Causes an Automatic Car to Stall?by Wanda Thibodeaux
In the transmission of an automatic car, there is a torque converter, which takes the place of a mechanical clutch. The torque converter is supposed to unlock both during cruising and deceleration. Sometimes, however, braking occurs before the torque converter has a chance to do this. The result is power loss and the stalling of the engine.
The idle circuit in an automatic vehicle controls the air that is circulated when the car idles. If this circuit malfunctions, then the vehicle may not have the right ratio of oxygen to operate. It will stall because the ratio is not optimal for the combustion of the fuel.
Most automatic cars have an oxygen sensor that keeps track of the oxygen levels in the air that is pushed out. Occasionally this sensor stops working properly and the vehicle is unable to determine that enough oxygen is available for combustion, so it stalls the engine.
If fuel is stale or has a high ratio of water in it, combustion is more difficult for the engine to achieve. No combustion results in engine stalling. Sometimes the octane rating of the fuel also makes a difference, because the octane level determines how hot the fuel burns.
Plugs and Wiring
If there is a problem with the spark plugs or within the wiring for the plugs, then sparks cannot be created that can ignite the fuel. If the fuel is not ignited, the engine can't run and will stall.