Car Sputters When Accelerating At Low Rpm (Below 2500): Let’s Debug!

Have you ever experienced the frustration of your car sputtering when accelerating at low RPM? You get in your car, turn the key, and start to drive.

Everything seems fine until you try to accelerate at low RPM. Suddenly, your car starts to sputter, jerk, and shake, and you feel like you’re driving a horse and buggy instead of a modern-day vehicle.

In this guide, we will delve into several reasons for which your car might sputter or jerk when accelerating at low RPM.

So, why car sputters when accelerating at low RPM? A car sputters when accelerating at low RPM because of a vacuum leak. This lets more air into the engine and mixes it with fuel poorly. This affects the combustion and makes your car sputter or jerk at low RPM. A bad ignition coil or spark plugs can also cause misfires and engine vibration, and cause your car to sputter. Other causes are bad MAF sensors, fuel filter, dirty throttle body, dirty air filter, or PCV valves.

Also Read: Car won’t accelerate but RPMs go up

How Does Engine RPM Change With Throttle?

Throttle input refers to how much you press down on the gas pedal. The more you press down, the more air and fuel flow into the engine, and the faster the engine rotates.

As a result, engine RPM increases with throttle input. This is because the engine needs more fuel and air to generate more power.

At idle, the engine is running at a low RPM, typically around 700-900 RPM for most cars. When you press down on the throttle, more air enters the engine.

As a result, the engine computer sends signals to fuel injectors to inject more fuel to balance the air-fuel ratio. As a result, the engine produces more power and RPM.

At idle, the engine is running at a low RPM, typically around 700-900 RPM for most cars.

However, it’s important to note that the RPM doesn’t increase in a linear fashion. Instead, the RPM curve is more exponential, meaning that the rate of increase in RPM decreases as you approach the redline.

This is because the engine becomes less efficient at higher RPMs, and it requires more energy to maintain each additional RPM. 

Also Read: RPM fluctuating at a constant speed

Causes Of Car Sputters When Accelerating At Low Rpm

Here are the causes of car sputtering or jerking when accelerating at low RPM:

1. Dirty Air Filter

An air filter is an essential component of the engine’s air intake system. Its purpose is to prevent dirt, dust, and debris from entering the engine and causing damage.

The air filter traps these particles as air flows through it, allowing only clean air to reach the engine. This clean air is then mixed with fuel and ignited, powering the engine and propelling the vehicle forward.

When an air filter becomes dirty and clogged, it restricts the flow of air to the engine. This decrease in airflow can cause a variety of issues, including reduced engine power, decreased fuel efficiency, and even engine damage.

One of the most common symptoms of a dirty air filter is a car sputtering when accelerating at low RPM or speeds. 

When the engine is running at low RPM, the flow rate of air with which it is entering the engine is low.

If the air filter is dirty and airflow is restricted to a significant extent, the low flow rate of the intake air is not able to overcome the restriction of the dirty air filter. As a result, air intake pressure decreases and your car will start sputtering at low RPM.

How to spot?

An engine air filter sits in the housing on the air intake side. You have to remove the engine cover to see that.

You should check the area below the air filter that sits in the housing. It is usually the intake side where outside air first passes through. So the dirt drops there after being sucked in. 

Determining if your engine air filter needs replacement can be done by checking its color.

Ideally, an air filter that’s still in good condition should be white or off-white. However, when it becomes dirty, its color changes to gray or black. In extreme cases of air filter neglect, it may turn brown or dark brown.

2. Vacuum Leaks

Vacuum leaks occur when air enters the engine through a path other than the throttle body. This extra air is called “unmetered air” because it is not being measured by the

Mass Air Flow (MAF) sensor or the Manifold Absolute Pressure (MAP) sensor. When extra air enters the engine, the air/fuel ratio becomes imbalanced, which can cause a variety of problems, including sputtering when accelerating at low RPMs.

The amount of air that enters the engine through the vacuum leak can vary, depending on the size of the leak and the position of the throttle.

When the engine is running, it creates a vacuum that draws in air, fuel, and exhaust gases. This vacuum is created by the downward movement of the pistons during the intake stroke.

When the engine is idle, the throttle plate is mostly closed, which restricts the amount of air that can enter the engine.

This creates a high-pressure area in the intake manifold and a low-pressure area in the engine’s combustion chambers. This low pressure is what creates the vacuum effect.

However, as you press the accelerator pedal, the throttle plate opens up, allowing more air to enter the engine. This increases the pressure in the intake manifold and decreases the vacuum effect. 

Since there is more vacuum in the engine at low RPM, if there is any vacuum leak, a substantial amount of “unmetered air” will enter the engine and disturb the air-fuel ratio. This will cause the car to sputter at low RPM.

Why there are vacuum leaks?

There are several potential causes of vacuum leaks in your engine. Here are some of the most common ones: 

• Damaged or Cracked Hoses: The most common cause of vacuum leaks is damaged or cracked hoses. The engine’s air intake hose is made of rubber and can become brittle over time, leading to cracks. These cracks create gaps in the intake system, allowing air to enter the engine without passing through the air intake system. This leads to poor engine performance. You should check the air intake hose that connects the throttle body to the air intake manifold.
• Worn or Damaged Intake Manifold Gasket: The intake manifold gasket is responsible for sealing the intake manifold to the engine block. Over time, this gasket can become worn or damaged, which can allow air to enter the engine from sources other than the air filter. 
• Cracked or Damaged Vacuum Hoses: The vacuum hoses in your engine are responsible for carrying air to and from various components, such as the EVAP purge valve, EVAP purge valve, fuel pressure regulator, and the PCV valve. If these hoses become cracked or damaged, they can allow air to leak into the system and cause issues.
• Throttle Body Gasket Failure: The throttle body gasket is responsible for sealing the throttle body to the intake manifold. If this gasket fails, it can cause a vacuum leak. The vacuum pressure can pull air into the engine through the gap in the gasket, causing the engine to run poorly. 
• Loose or Damaged Fuel Injector O-Rings: Fuel injectors are responsible for delivering fuel into the engine. They are sealed using O-rings, and if these O-rings become loose or damaged, it can allow air to enter the engine, leading to a vacuum leak.

If there is a vacuum leak, you will hear a hissing noise from the engine.

You can use carb cleaner to detect vacuum leaks in the engine.

3. Damaged Ignition Coil

The ignition coil works by using two coils of wire, the primary and the secondary coil. The primary coil is connected to the battery, while the secondary coil is connected to the spark plugs.

The terminals of the ignition coil in which the harness connector is plugged are the terminals of the primary coils of the ignition coil.

When electricity flows through the primary coil, it creates a magnetic field that is then transferred to the secondary coil. This magnetic field creates a high voltage that is required to ignite the fuel and air mixture in each cylinder. 

When the ignition coil is damaged, it can cause your car to sputter when accelerating at low RPM/speeds.

This is because the damaged ignition coil is not producing enough voltage to ignite the fuel and air mixture in the engine’s cylinders.

As a result, the engine may misfire or hesitate, causing the car to sputter. Other symptoms of a damaged ignition coil include difficulty starting the engine, rough idling, and poor fuel economy.

There are three types of ignition coils that are commonly used in engines today: distributor, coil pack, and COP (coil-on-plug) ignition coils. The type of ignition coil used in an engine depends on the make and model of the vehicle. 

A distributor-based ignition system is found in older vehicles. It uses a single ignition coil to generate high voltage, which is then distributed to each spark plug via a distributor cap and rotor. The distributor cap and rotor work together to ensure that the high voltage is delivered to the correct spark plug at the right time. 

The ignition oil is connected directly to the rotor, and the rotor spins inside the distributor cap. The rotor is attached to the shaft of the gear drive. The gear drive is driven by the camshaft.

On the underside of the distributor cap, a spring-loaded carbon brush contacts the metal part of the rotor.

The distributor shaft rotates when the camshaft rotates. As a result, the rotor attached to the distributor shaft also starts rotating. As the outer edge of the rotor passes each internal plug terminal in the distributor cap, the spark plugs will fire in the correct order.

Coil pack ignition coils consist of a single unit that contains multiple ignition coils. Each coil is responsible for generating the high voltage required for a single spark plug. Coil pack ignition coils are located near the engine and are connected to the spark plugs through short high-tension wires.

COP (Coil over plug) ignition coils are also commonly used in modern engines. They are similar to coil pack ignition coils, but instead of a single unit, each ignition coil is located directly on top of the spark plug. This design eliminates the need for high-tension wires and ensures a more efficient spark.

How do ignition coils go bad?

You check the ignition coil for any physical damage. Look for cracks, corrosion, or any signs of wear and tear.

Moisture and other contaminants can also get into the ignition coil, causing corrosion. This can weaken the coil’s windings, leading to a reduction in the voltage output.

You should check also the coil’s wire and connector for signs of corrosion or damage. If the connector of the ignition coil is corroded, it can cause a poor connection, leading to a weak spark.

The next thing you can do is started swapping ignition coils one by one and see if car sputtering goes away or not.

If your vehicle has a distributor, the contacts inside the distributor cap can become corroded or worn down, which can lead to a weak or intermittent spark.

The rotor can also wear down over time, which can cause it to make poor contact with the contacts inside the distributor cap.

For the ignition coil pack, follow the below video:

The final step is to test the resistance of the ignition coil using a multimeter. Set the multimeter to the “ohms” setting and touch the probes to the coil’s terminals.

The resistance should be within the range specified by the manufacturer. If the resistance is too high or too low, it’s a sign that the ignition coil is faulty and needs to be replaced. 

4. Fouled Spark Plugs

Spark plugs are a crucial component of a car’s ignition system. They ignite the fuel mixture in the engine’s combustion chamber, which powers the vehicle.

Over time, however, spark plugs can become fouled, which means that they are covered in a layer of foreign material that prevents them from functioning properly. This can result in a variety of issues, including a sputtering car when accelerating at low RPMs. 

Why do spark plugs go bad?

Fouling can be caused by a variety of factors, including:

• Worn piston rings or valve seals: These can cause oil to leak into the combustion chamber and coat the spark plug.
• Rich fuel mixture: An overly rich fuel mixture can cause unburned fuel to coat the spark plug with carbon. The rich fuel mixture can be caused by bad fuel pressure regulator and leaking fuel injectors.
• Wear and Tear: Like any mechanical component, spark plugs can wear out over time. The electrodes on the plug can become worn down, reducing their ability to produce a spark. Additionally, the ceramic insulator that surrounds the electrode can crack or break, causing a loss of spark energy. The ceramic insulator of a spark plug serves as a dielectric barrier that prevents the electric current generated by the ignition coil from shorting out and reaching the engine block. If the current were to reach the engine block, it would cause a short circuit and damage the engine’s electrical system. 
• Heat Damage: Spark plugs operate at high temperatures, and over time, this heat can cause damage to the plug. The electrode can melt or become distorted, reducing the spark’s effectiveness. 
• Improper Gapping: Spark plugs are designed with a specific gap between the center and ground electrodes. If the gap is too small or too large, the spark plug may not fire correctly, causing engine misfires, rough idle, and reduced power. To diagnose improper gapping, use a feeler gauge to measure the gap between the electrodes. If the gap is too small or too large, adjust it to the manufacturer’s specifications.
• Blown head gasket: It causes coolant to leak and foul spark plugs.

To find out how the spark plug is fouled, you need to remove it using the spark plug socket. After that, visually inspect the spark plug to see how it was fouled.

You can take help from the spark plug trouble tracer chart (PDF download) to learn more.

How to fix?

Instead of cleaning the spark plugs, I would suggest them to replace. Spark plugs are quite cheaper to replace without taking help from a mechanic. Just make sure that you use OEM spark plugs with the correct gap between spark plug electrodes.

5. Bad MAF Sensor

The Mass Air Flow (MAF) sensor is located in the air intake system before the throttle body and measures the amount of air entering the engine. This information is then sent to the engine control module (ECM), which uses it to calculate the correct amount of fuel to inject into the engine for optimal combustion. 

MAF does this by using a heated wire or film that is cooled by the incoming air. As the wire or film cools, its electrical resistance changes, which the ECM then uses to calculate the amount of air entering the engine.

If the MAF sensor fails or becomes dirty, it can send incorrect readings to the ECM, causing the engine to sputter.

How to fix?

As the mass flow rate of air through the MAF sensor increases, voltage output also increases. As you press the gas pedal, more air passed through the MAF sensor. As a result, voltage output increases.

At idle, the voltage should be less than 1.0V. As you increase RPM, the voltage output by the MAF sensor increases from 1.0V to 1.7V. 

If the MAF sensor is dirty or covered in debris and its voltage is fluctuating, it may be possible to clean the heated element of the sensor using a specialized cleaning spray. I would recommend this cleaner. If your vehicle has a MAP sensor, it can’t be cleaned. You should replace it.

Here is a short YouTube video explaining how to clean an MAF sensor:

Car Sputters When Accelerating At Low RPM: FAQs