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Four common causes for a vehicle jerking when driving at low speeds and their related parts.

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Is Your Car Jerking When Accelerating at a Low Speed?

The jerking happens because of a problem in the engine's fuel flow, typically caused by dirty fuel injectors, broken spark plugs, or faulty ignition coils. Jerking can also occur due to other factors, like debris in the mass airflow sensor, damaged plug wires, or a faulty throttle position sensor.

Watch out: Maintaining your vehicle's well-being is not merely a convenience; it also ensures your safety and peace of mind. These sudden jolts prevent your car from maintaining a constant speed, affecting its reliability. By promptly addressing the jerking issue, you can prevent potential complications and regain your confidence on the road.

The most common causes for a vehicle jerking when accelerating at low speeds

The most common causes for the car jerking when accelerating at low speeds:

Faulty ignition coil: The ignition coil is an electrical component in the engine that transforms low-voltage battery power (12 volts) into the high voltage (thousands of volts) needed to create a strong electric spark at the spark plugs. It basically acts as a transformer that strengthens the vehicle’s voltage. However, if the coil fails, this electrical spark might become weak, uneven, and out of rhythm, resulting in engine misfires and sputtering.
Damaged spark plug wires:
Dirty Mass Airflow Sensor: The mass airflow is the amount of air that enters the engine during combustion, which is measured by the Mass Airflow Sensor. This component makes internal calculations to understand how much air is entering the engine so it can determine how much fuel to inject, making combustion work its best. However, if this component fails, these air calculations go wrong, resulting in the engine struggling to combust efficiently, causing jerkings when accelerating.
Dirty Fuel Injectors: The fuel injectors constantly spray fuel inside the combustion chamber while the vehicle drives, so it can provide the needed fuel based on engine demands. However, if the fuel injectors go faulty due to wear, damage, or carbon deposits, the fuel demand won’t succeed, resulting in engine misfires and combustion-related vibrations.
Faulty spark plug: Spark plugs are components inside the engine that ignite the air-fuel mixture in the combustion chamber by creating a small electric spark. This spark causes a mini-explosion when contacting the fuel that powers the engine. However, when spark plugs fail, these sparks might lose rhythm or time, resulting in engine misfires and sputtering.
Faulty Throttle Position Sensor: The throttle body is a component that controls the amount of air that enters the engine; it’s an airflow component from the vehicle’s cooling system. Therefore, the throttle body is essential for managing vehicle temperature and it works by opening and closing a valve based on whatever the driver is doing with the accelerator. This way, the valve opens to allow air inside the engine during acceleration, so combustion can work its best to provide power. However, this movement depends on a sensor, which picks up the throttle inclination while the driver presses the pedal. This sensor, the Throttle Position Sensor, is the only component generating the information that the Throttle Body needs. Therefore, if the sensor fails, the body fails too, resulting in jerky movements when driving.

Frequently Asked Questions

Is the vehicle's "check engine" light active on the dashboard?

The mass air flow sensor tracks how much air goes into the engine. It tells the passing air volume and speed to the engine's computer. This helps the system determine how much fuel the engine needs to run smoothly, enabling enough power and speed. It also helps reduce pollution. But if the mass air flow sensor doesn't measure the air correctly, other sensors in the engine and exhaust will notice something's off and tell the computer; this can happen due to debris or wear. Then, the check engine light will turn on as a warning. At this stage, the car might commonly sputter when accelerating.
Have the vehicle's fuel economy suddenly worsened?

In a gasoline car engine, small parts called "fuel injectors" spray fuel into the engine before it ignites. Over time, these parts can get dirty and clogged from lack of maintenance. If that happens, the injector won't be able to spray the fuel, only dribble it out, making it harder to ignite. This causes the fuel to not burn completely in the engine cylinder, leading to lower performance and fuel economy.
Is the engine idling rough?

Idling rough is when the engine runs unevenly or inconsistently when the vehicle is standing; this can happen due to damaged spark plug wires. Spark plug wires are responsible for carrying high voltage to the spark plug, which creates a spark to ignite the fuel in the engine cylinder. If these wires become brittle, cracked, or damaged, the high-voltage spark can short to the ground instead of reaching the spark plug. In the future, this damage can result in faulty spark plugs. This prevents the cylinder from firing properly, resulting in a rough idle and car jerks when accelerating slowly.
Is the "check engine" flashing on the dashboard and the car struggles to start in cold weather?

The spark plugs in your car help light a small fire inside the engine that makes it go. But spark plugs have a tough job because they must work in hot and harsh conditions. As you use your car, the spark plugs will wear out over time, and the gap will get bigger. This can make them weaker and not as hot, which can cause problems. When it's freezing outside, this problem gets even worse. If your spark plugs are already worn out, your engine might not be able to start at all, or it might run rough until the engine warms up.
Is the "check engine" warning lighting up when you accelerate?

The ignition coil is an essential component of your car's engine that converts low voltage into high voltage in the battery, igniting the spark plugs. The high-voltage side of the coil requires good insulation to avoid going to the ground instead of the engine's spark plug. If the insulating boot between the coil and spark plug gets damaged, cracked, or soaked with oil or coolant, it causes the coil to short-circuit and fail. If the coil fails, the engine computer detects a misfire and triggers the check engine light on the dashboard.
Is the vehicle idle surging?

Idle surging is an irregular fluctuation in engine speed while the vehicle is stationary and not in motion. This is managed by the throttle position sensor, which detects the position of the throttle plate in the engine. If it malfunctions, the engine's computer may have difficulty accurately controlling the idle speed, leading to unstable idle and surging.

Typical fixes to address the cause(s)

These are typical processes and repair services that fix a check engine light issue

The most common cause: Dirty Fuel Injectors

The most common reason for a car jerking when accelerating at low speeds is due to clogged fuel injectors causing combustion problems. The fuel injectors are constantly spraying fuel inside the engine during combustion. In a crude summarized way, fuel is like nutrition for the engine, giving it power. However, fuel needs to be balanced with air; the engine gets the best of combustion when it has a precise balance of fuel + air. If a fuel injector is clogged, it'll spray less fuel, and the engine starts working with more air than fuel. Consequently, the combustion process gets issues and the engine sputters.

Symptoms it causes: Apart from the vehicle jerking when accelerating at low speeds you might notice engine misfires, engine sputters, rough idling, engine stalling, lawnmower noises, etc.
High risk of priority: A dirty fuel injector can obstruct the fuel flow inside the engine, leading to combustion issues. Consequently, the engine might misfire, lose performance, consume fuel excessively, stall, or even break down, in the worst cases.

How exactly do fuel injectors clog up?

Fuel injectors naturally clog up because they're constantly working with fuel; fuel leaves carbon residues when it doesn't burn completely. This process is very minimal and takes long to clog up fuel injectors. However, it can happen faster depending on bad vehicle maintenance, driving habits, or other issues that trigger it.

Go safe: Ask for a mechanic to inspect your vehicle’s combustion system to investigate if the fuel injectors are dirty due to surrounding components and if there’s further damage to check out. Many shops do transparent vehicle inspections and lay out your options after investigating your vehicle’s conditions.

What’s a vehicle inspection? It’s “detective work” on your vehicle, checking its systems to see if anything prevents the car from working as expected. In this case, mechanics examine different parts of your vehicle to track if anything is causing the fuel injectors to become dirty. They’ll also check the condition of components during their inspection, noting which are causing the problem and which got affected by it, recommending to replace them in order of priority.

Transparency example in a bad air filter service

A combustion system inspection is the most transparent process to understand why your vehicle’s fuel injectors are clogged. This is because many components surrounding the injectors and air intake components can have a say in the issue, indicating the real culprits that caused it all.

Let’s read an example of how this kind of inspection helps to service a clogged fuel injector and solve a jerking when accelerating at low speeds issue.

When the customer brought in their vehicle, they expressed concerns about the dropping fuel economy. They were unsure if it was due to the gas quality or an issue with the vehicle.

During the test drive, the technician didn't notice anything about the customer's concern. Furthermore, during the vehicle health inspection, nothing showed what was causing a decrease in fuel economy.

With the customer's authorization for additional diagnostics, the technician used a specialized scanner for this vehicle. They checked for any trouble codes in the vehicle's modules but found none. While monitoring the live data, the technician noticed the calculated load was higher than normal.

Upon inspecting the throttle body, the technician found clogged and dirty fuel injectors. Therefore, the technician recommends a gas direct injection fuel service to address this issue and improve air-fuel mixture. This service involves cleaning the throttle body and the injectors.

The customer agreed to proceed with the recommended service, and after it was performed, the calculated engine load dropped by 10% and returned to the normal range.