Possible Causes Why Your Car Engine Sputters At Low Speeds

If you drive a manual transmission car, you probably already know about the sounds that your engine makes in association with the amount of gas you give it. There is frequently a sputter or deep rumble at the speeds that are very low. However, when these sounds start becoming more frequent when you drive, or if you have started to notice these sounds in an automatic-transmission vehicle, this might be an indication that your vehicle requires a tuneup.

The Differences Between High And Low Speeds In Engines

There are a number of forces that work together in an engine that translates into speed when you are driving your car. The primary ones include RPM which stands for revolutions per minute and torque.

An example of RPM and torque can be compared to using a screwdriver in order to drive screws into a piece of wood. The resistance is at its highest when you first start, which means it takes more energy and power to get your screw started. Once the screw starts to turn, it typically eases up slightly, while the circular motions are what assists with carrying the force. This means you eventually start adding less torque energy levels to keep the screw going. This translates into the power of RPM. As soon as you increase the RPM in your screw, it will start to drive into the piece of wood at faster speeds.

Vehicles operate in a very similar way. Even though it requires more force in order to start moving forward, as the engine starts gaining momentum through RPM, it starts carrying itself. This is also the reason why a car starts to accelerate faster once it reaches higher speeds. The one requirement to this particular correlation will be that the car needs to change gears as soon as it reaches a peak RPM (In an automatic transmission the car switches gears on its own, while in manual transmissions you will need to change the gears). If you fail to shift into the next gear, the car will start to over accelerate, which could result in damages to your engine, by pushing the vehicle to speed up.

The Common Causes Of Car Engine Sputters

The main reason behind engine sputtering is caused by the wrong combination of fuel and air inside your engine. This issue can arise from a number of different sources which usually depend on the car type and age. Here is a list of the more common reasons why your car engine sputters at low speeds.

1. Faulty Spark Plugs

Spark plugs are necessary to provide ignition to the fuel/air mixture. However, these plugs can wear out, which means they are no longer functioning as they should. If this is the case, there will be a lot of fuel that is unburnt that will cause misfires, which causes your engine to start sputtering. At your next scheduled service make sure that you have the plugs replaced. One or more spark plugs that are faulty will result in misfires, which is also classified as sputtering.

2. An Issue With Your Accelerator Pump

If your car is older and it features a carburetor, there could be an issue with the accelerator pump, which provides the intake-manifold with additional fuel that is required under low RPM.

3. Dirty Fuel Injectors

The fuel injectors in a car perform the function of spraying the fuel into combustion chambers. This then mixes with air, which is then ignited by your spark plugs. If your fuel filter is old and dirty, then less fuel goes into these combustion chambers. This usually causes slower acceleration. You can choose to have the fuel injectors cleaned to solve this issue.

4. Problems With Your Electronic Fuel Injection System

The newer cars are typically accelerated by an Electronic Fuel Injection System (EFI). If your car was produced after the year 2000, then your Electronic Fuel Injection might be misinterpreting one of the sensors. There are 3 sensors you should check on and these include the Mass Airflow Sensor, the Manifold Absolute Pressure Sensor, and the Throttle Position Sensor.

5. Dirty Mass Airflow Sensor

The combustion chamber in your vehicle necessitates the correct amount of air and fuel. The more modern engines feature onboard computers which monitor how these components flow. The Mass Airflow Sensor performs the function of ensuring the correct air amounts are supplied into your combustion chambers.

If these sensors become saturated with dust or dirt particles, they are not able to relay this information to an onboard computer system. This usually means that less air will be flowing into your combustion chambers, which causes the car to start sputtering at low engine speeds. This is an issue that is easy to solve by having these sensors cleaned.

6. Problems With Your Ignition System

Another common cause of the incorrect fuel and air mixture has to do with your ignition system, and more specifically the ignition coil, plug wires, and the spark plugs. These components may have become wet, grown weak, or dirty. In addition, there may be clogged filters, which stops the airflow needed to encourage combustion.

7. Vacuum Leak

Your car also features vacuum hoses, that can over time start to develop leaks. This also contributes towards car engine sputters when either the fuel or air mixture becomes too lean or too rich.

8. Faulty Catalytic Converter

The catalytic converter in any car performs an important role when it comes to the removal of harmful gases out of the exhaust. If your catalytic converter is no longer functioning the way it should, some of the gases will flow into the tailpipe. One of these gases is sulfur which should be broken down, due to its harmful effects on the environment.

If the catalytic converter on your car is not functioning very well, it is possible to start noticing a pungent odor similar to rotten eggs. If you fail to conduct the necessary repairs for your catalytic converter it will eventually break down and your car will stop working.

9. Exhaust System Leaks

The combustion engine (internally) works with ignition from a mixture of air and fuel. The exhaust gases that are produced are known as byproducts. These byproducts then flow into the manifold and then into the surrounding atmosphere. The catalytic-converter plays an important role to remove harmful compounds from your exhaust such as carbon monoxide and hydrogen monoxide.

The gas is converted into inert gases which are less harmful. If your exhaust system has sprung a leak, these gases start to escape before reaching the tailpipe. This is when you will start to hear sputtering sounds. This situation can become worse as these exhaust gases happen to be extremely hot, which can cause other components in your car to start melting.

10. Dirty Oxygen Sensors

Many of the latest cars all have onboard computers that are designed to monitor every engine component. Connected to all of this is the Oxygen Sensors that regulate the fuel that enters the Combustion chambers. If this sensor is faulty it will either result in a lean or rich mixture.

Over time these Oxygen Sensors get contaminated with dirt particles, which means they are unable to relay information to your onboard computer. This usually results in the release of too little or too much fuel. You should be changing your oxygen Sensors every now and again.

11. Worn Out Gaskets Or Seals

The gaskets and seals are what stop oil and exhaust gases from getting inside the Combustion chambers. If either of these components fails you will start to notice that your car engine sputters at low speeds. If the seal damage becomes extensive it can lead to the eventual destruction of your exhaust manifold. Always replace the gaskets and seals as soon as you discover a leak or ask your mechanic to check on them at each scheduled service.

Tips On How To Correct Engine Sputtering

You can usually change filters by yourself and they are usually inexpensive. Yet if you drive one of the newer cars that comes with sensors, you will need diagnostic tools in order to isolate the issue that is causing your engine to sputter. If you try to fix these issues on your own in order to save a bit of money, it could end up costing far more due to trial-and-error processes. When you decide to take your sputtering vehicle to a reputable and reliable auto technician, in most cases the issue will be solved on the same day.


An engine that starts to sputter can be concerning for both new and old motorists. It could range from anything that includes clogged fuel injectors to faulty catalytic converters. Regardless of what the issue might be as to why your car is spluttering at low engine speeds, it is always recommended to take your car to your closest mechanic or auto technician so that they can conduct the necessary tests in order to find the source of the exact issue.