Why Your Car Sputters When Starting But Then Runs Fine


Car engine problems are pretty mysterious and hard to understand if you’re not used to them. For example, why would a car sputter when you start it yet run fine after a few moments? This guide will help you understand the answers to that question.

An engine will sputter when the air/fuel mixture isn’t combusting completely in its chambers. That can happen due to a weak car battery, dirty or faulty sensors, or a bad fuel pump. The same can also occur when the ignition switch malfunctions or any of the car’s filters are clogged.

Like many other car problems, engine sputtering is best resolved quickly before it gets worse. So, this guide will help you understand how serious car sputtering is, why it happens, and how you can fix it quickly.

Is Car Sputtering Serious?

Engine sputtering happens when combustion isn’t happening correctly inside its chambers. 

The sputtering by itself isn’t serious, so there’s no need to panic if your car suddenly does it. That’s especially true if the sputtering only happens as a one-off occurrence when starting your car. 

However, continuous sputtering is a clear symptom of an underlying problem that you should not ignore. While the sputtering might not be serious, the underlying problem will become a significant issue if you don’t sort it out quickly.

Remember: always resolve car problems while they are minor. Ignoring them will lead to more significant and more expensive repairs later.

When you notice your car sputtering, it’s best to take it to your mechanic for them to troubleshoot the problem and rule out any significant issues.

What Causes A Car To Sputter Only When Starting?

As you read above, a car sputters when the engine can’t combust its fuel and air mixture completely. Here’s why that happens only when starting the vehicle before it runs fine:

1. Weak Car Battery

The first reason for sputtering while starting is a weak car battery. The battery is critical for the smooth start of your car engine.

Firstly, the battery delivers power to the starter to crank the engine. Simultaneously, the battery also powers the spark plugs to ignite the air and fuel mixture inside, kickstarting the combustion process.

Many companies take over once the engine is running. However, everything begins with the car battery when you turn the key in the ignition.

Related: How Long Can a Car Battery Sit Unused?

What’s gone wrong:

The sputtering is caused by a weak car battery, i.e. one that isn’t holding enough of an electrical charge to start the car engine smoothly.

There are two reasons why a car battery is weak. Firstly, the battery might have discharged most of its power while the engine was off, perhaps due to the headlights being left on.

Besides that, an old battery is naturally unable to hold much of a charge, to begin with. Both issues will cause sputtering when starting the engine.

How to fix it:

A weak battery can be recharged, either by taking the car for a 15-30 minute drive or by connecting it to a battery charger.

Unfortunately, old batteries must be replaced with new ones. The sputtering could be an early sign that the battery is reaching the end of its life.

2. Dirty Or Faulty Sensors

Your car relies on plenty of sensors to function correctly. The combustion process relies on 3 sensors in particular: the oxygen sensor, the mass airflow sensor, and the fuel injection sensor.

The data collected by these sensors enable the engine to decide on the correct fuel-to-air ratio for optimal combustion.

What’s gone wrong:

Sputtering can also be caused when one or more of the sensors mentioned above becomes dirty or faulty.

Remember: the engine controls its fuel/air mixture based on the data provided by those sensors. Faulty sensors provide incorrect data, causing the engine to use an incorrect fuel-to-air ratio, which then causes it to sputter.

How to fix it:

The oxygen, mass air flow, and fuel injection sensors must be inspected closely. Dirty ones must be cleaned thoroughly, but faulty ones must be replaced immediately.

3. Bad Fuel Pump

The fuel pump has an incredibly straightforward purpose: it takes fuel from the gas tank and drives it through the lines towards the engine. When the fuel pump is clean and works correctly, the engine will have a reliable fuel supply to function continuously.

What’s gone wrong:

Sputtering is caused by incomplete combustion in the engine’s chambers. Unfortunately, that can also be caused by a bad fuel pump that fails to drive fuel through the system towards the engine.

As a result, the engine gets an intermittent supply of fuel that you experience as sputtering while starting the vehicle.

Related: What Happens When the Fuel Pump Goes Out? 

How to fix it:

This problem will require a thorough inspection of the fuel pump done by a qualified technician. They’ll need to inspect the pump to ensure it’s free from any clogs and can function correctly.

The pump might need to be replaced if it no longer works as it should.

4. Ignition Switch Malfunction

The ignition switch controls the power supply between the car battery and the engine starter. So, the switch powers the starter to crank the engine whenever you turn the key in the ignition.

What’s gone wrong:

Sputtering that only happens when starting the engine also suggests a problem with the ignition switch. The concept is somewhat similar to the fuel pump discussed in the previous section.

While the faulty fuel pump interrupts the engine’s fuel supply, a malfunction in the ignition switch interrupts the starter’s power supply.

As a result, the starting process is interrupted, and sputtering occurs.

How to fix it:

An ignition switch doesn’t malfunction often. So when it does, that’s a sign that it might be approaching the end of its lifespan and need a replacement.

A mechanic can tell you if it needs repairs or a complete replacement.

5. Clogged Filters

Lastly, you must also consider the filters in your car. That includes the air filter, fuel filter, and engine oil filter. Each is designed to ensure that anything entering your engine, whether fuel, oil, or air, is free from contaminants.

What’s gone wrong:

Sputtering can also be caused by a clog at one or more of the filters mentioned above. Filters saturated with contaminants will prevent the engine from getting the initial flow of air, fuel, or oil, which causes it to sputter when starting.

However, the car will run fine after a few moments once those things can flow somewhat smoothly through the dirty filters.

Related: Can A Clogged Fuel Filter Cause A Misfire Or Rough Idle?

How to fix it:

Any filter can be cleaned as part of its regular maintenance. However, suppose it’s clogged so severely that it leads to sputtering. In that case, it’s likely time to replace that filter with a new one so your engine can function optimally.

Final Thoughts

As you can see, the reasons why a car sputters when starting but then runs fine aren’t severe or catastrophic for the engine. However, they will become severe and disastrous if you do not fix them soon enough.

So, troubleshoot any sputtering as soon as you notice it or take the car to a mechanic so they can do it for you. Whatever price you pay to do so will pale compared to the repairs and parts replacements you’ll have to do if those problems worsen.

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