Moisture in the distributor cap can cause a car to jerk when accelerating. When a car has been parked overnight in cold temperatures, moisture can form inside the distributor cap, causing the engine to misfire when accelerating. A misfire occurs because the engine power is off balance or uneven. Parking a vehicle in a garage or a warmer environment helps prevent moisture from forming.
If the vehicle continues to jerk while accelerating gradually over a prolonged time period, a vacuum leak may be the cause. A vacuum leak occurs when the fuel system creates a vacuum in the engine, causing the vehicle to spring forward when the gas pedal is pushed. The vacuum leak sends an incorrect amount of fuel to the engine, causing the vehicle to jerk when accelerating.
If the vacuum leak is not the cause, a car may also jerk when accelerating if it has a faulty throttle position sensor. This occurs in vehicles equipped with a fuel-injection system. Once the gas pedal is pushed, the data in the sensor allocates a certain amount of fuel to disperse. When the throttle position sensor is faulty, it transmits incorrect data, which in turn sends the wrong amount of fuel to the engine.