Automatic Car Jerks When Stopped At Light? [ Here’s Why ]

Do you experience car jerking while stopped at a red light or parking? Sometimes even new cars jerk whenever sitting idle or stopped at a location. The entire vehicle lurches forward as if something is hitting it from the back. That sounds annoying, doesn’t it?

Although car jerks irritate you while driving, these are not as uncommon as you might think them to be. If you wish to know the reasons behind this problem, you have landed at the right place. We have researched this thoroughly to get you an answer.

Why do car jerks when stopped at a red light automatically?

A car jerk is most commonly due to a faulty coil pack or a dirty throttle body. One of these issues is the primary reason your car jerks when stopped somewhere.

The throttle body controls the airflow throughout the engine of your vehicle. It behaves erratically, when damaged or gets dirty. The car will jerk at odd times, and this essential equipment will not function well. You can clean the throttle body to resolve this issue.

Another likely cause of a car jerk is a faulty coil pack. Newer cars use coil packs instead of the traditional distributors. A defective coil pack causes one or more of your car’s cylinders to fire or not to fire at the correct time. In many models, this is the chief cause of a car jerk.

What are the other reasons?

The other causes of a car jerk are a dirty fuel injector, weak battery, clogged air intake, bad alternator, worn spark plugs, engine vacuum, bad speed sensor, and bad mass airflow sensor. Let us discuss some of these in detail below.

1. A dirty fuel injector

A professional mechanic can quickly fix this issue. A dirty fuel injector means your engine is not getting sufficient fuel, leading to misfires, jerking, and bucking. Some symptoms of a dirty fuel injector are rough idling, clogged air, and poor acceleration.

2. A bad battery

If your vehicle’s alternator fails to provide the correct amount of electrical energy for proper functioning, the car will take the rest of the energy from the battery. You will experience jerking if the battery fails to provide the remaining amount of electrical energy.

A low supply of electrical energy negatively affects the spark plugs. The job of spark plugs is to ignite the fuel and air mixture inside the combustion chamber.

They cannot perform their functions well in case they get insufficient electrical energy. It will cause an improper burning of the fuel and air mixture.

3. Clogged air intake

The car engine needs the correct amount of fuel and air to produce energy for working. A clogged air intake limits the amount of air that gets into the engine.

You may also notice the smell of gasoline inside your car when this happens. One of the malfunctions of a clogged air intake is the jerking of the vehicle.

4. A bad speed sensor

A speed sensor measures the speed of your car at the transmission level. The Engine Control Module or ECM uses this data to calculate the correct fuel-air ratio, shifting point of transmission, and ignition timing.

Once the speed sensor goes faulty, the car’s automatic transmission will perform poorly.

Automatic transmission will face delayed shifting, hard shifting, and limited operation of the gears. A poor speed sensor also measures data inaccurately. Due to this, the ECM calculates the wrong fuel-air ratio, resulting in jerking.

Bottom Line

A car can jerk when stopped at a red light for several reasons, but the primary cause is a faulty coil pack. You can use an active warranty on your car and replace the damaged parts. A professional mechanic will determine the cause of jerking in your vehicle.