Problems with acceleration, engine misfires, reduced fuel mileage, stalling and difficulties starting the vehicle are all possible symptoms of a bad crankshaft sensor, according to 1A Auto. A bad crankshaft sensor may also cause the vehicle to idle roughly or make the check engine light come on.
One of the functions of the crankshaft sensor is to provide information to the engine control unit as the vehicle speeds up, which allows the control unit to make the proper adjustments to the fuel injection and spark plug timing. If the sensor is bad, it cannot provide accurate input to the control unit, which can cause slow or uneven acceleration. This problem can also cause the vehicle to use more gas with the fuel injection system working inefficiently, resulting in lower gas mileage. One or more of the engine's cylinders may also sometimes misfire due to the improper spark timing.
In some cases, the crankshaft sensor problems are worse when the vehicle is travelling slowly or idling, which is due to issues in the spark timing. This can cause the vehicle to idle roughly or even stall out at slower speeds due to the lack of fuel injection. If the vehicle won't start or is difficult to start, it could also be a sign that the engine control unit isn't properly receiving input from the sensor.