Car Idles Fine but Sputters When Accelerating (Causes & Fixes)

Jos Fallon
Car Idles Fine but Sputters When Accelerating

Does your car idle smoothly but struggle when you hit the accelerator? You’re not alone. Many drivers experience this frustrating issue, making driving feel like a chore.

In most cases, the sputtering results from clogged filters or a bad fuel delivery system (fuel injector or fuel pump). However, it can also occur due to malfunctioning sensors, bad spark plugs, or exhaust issues.

Further, in this article, we will uncover all the hidden culprits behind the sputtering and help you resolve the issue with the necessary fixing steps.

10 Causes Why a Car Sputters When Accelerating

Sputtering refers to an engine’s rough or uneven running. Intermittent power loss, misfires, or hesitations during acceleration often characterize it. When a car sputters, it may feel like the engine is struggling to maintain consistent power, failing to accelerate over a certain speed. It may also jerk or shudder as a result.

Sputtering usually accompanies unusual engine or exhaust system noises, such as coughing, popping, or backfiring sounds.

The fuel delivery system is the culprit, but multiple other factors can cause this. Let’s explore them one by one.

Cracked Expansion Tank

1. Clogged Fuel Injectors

Fuel injectors deliver the precise amount of fuel needed for combustion.

It is commonly observed that they can catch dirt or debris with time. This impedes their ability to provide the correct amount of fuel, causing the engine to sputter when accelerating.

Fix: Use a quality fuel injector cleaner to remove deposits and improve performance. Consider having a professional mechanic clean or replace the injectors if the issue persists.

The fuel injector replacement costs between $300 to $1000.

2. Blocked Fuel Filter

The fuel filter eliminates the contaminants from the fuel before they reach the engine. When the filter gets clogged, it restricts the flow of fuel, causing sputtering when the engine demands more fuel during acceleration.

Fix: Check out the fuel filter and replace them every 40,000 miles. They are not costly, and their replacement costs remain $200, even in extreme cases.

3. Failing Fuel Pump

The fuel pump delivers fuel from the tank to the engine at the designated pressure. It usually fails after the car has traveled more than 100,000 miles.

A failing fuel pump does not provide the necessary fuel pressure, leading to a lean air-fuel mixture. This consequently causes the engine to sputter during acceleration.

Fix: Test the fuel pump for proper function and replace it if necessary. You will need to check its pressure with a fuel gauge. The nominal pressure is 4 to 7 bar. If the fuel pressure is lower, the pump needs a replacement.

This typically would cost you $500-1000, including labor costs.

4. Worn Spark Plugs

Spark plugs ignite the air-fuel mixture in the engine’s cylinders. Over time, they can become worn or fouled, resulting in weak or inconsistent sparks. This can cause sputtering during acceleration.

Fix: Inspect and replace worn or fouled spark plugs as needed. For most people, it’s an easy job. However, if you’re unsure of their placement or don’t have the necessary, we don’t recommend you try this fix.

Dirty spark plug

5. Malfunctioning Mass Air Flow Sensor (MAF)

The MAF sensor measures the air volume entering the engine before combustion. Its value is to calculate the fuel amount according to the stoichiometric air-fuel ratio.

A faulty MAF sensor will send inaccurate readings, resulting in poor combustion and sputtering during acceleration.

Fix: Clean or replace the MAF sensor if it’s malfunctioning. Cleaning can sometimes resolve the issue, but a replacement may be necessary if it’s faulty.

6. Throttle Position Sensor (TPS) Malfunction

The TPS monitors the position of the throttle, providing information to the engine control module (ECM) to determine the optimal air-fuel mixture. A malfunctioning TPS can cause incorrect readings, which leads to inconsistent air and fuel supply. This causes incomplete combustion and hence sputtering.

Fix: Test the TPS for proper function and replace it if necessary. The best way to check if it is malfunctioning is with an error scan tool like OBD. A faulty TPS throws error codes P0122 and P0133. 

7. Damaged Gas Lines

Gas lines transport fuel from the tank to the engine. Damaged, leaking, or corroded gas lines can restrict fuel flow or introduce contaminants into the fuel system. This not only causes sputtering, but it’s also quite dangerous driving with this condition.

Fix: Take your car to a garage for a thorough inspection. A professional will examine the gas lines for damage, corrosion, or any leaks and replace them,

8. Possible Vacuum Leak

Vacuum leaks occur when the engine’s intake system is breached, allowing unmetered air to enter. This can disrupt the air-fuel mixture when the car is moving. Consequently, the engine runs lean and sputters during acceleration.

Fix: Manually check the vacuum leaks and intake manifold. If you find any cracks or leaks, act promptly and get them checked by a professional mechanic.   

9. Exhaust System Issues

A clogged or damaged exhaust system produces backpressure, which impedes engine performance and leads to sputtering when accelerating. Problems with the catalytic converter, muffler, or exhaust pipes can contribute to this issue.

Fix: Inspect your catalytic convertor to see the blockage. You may clear out some, but for most tailpipes, you will need a technician for a detailed inspection.

10.  Failed O2 Sensor

The O2 sensor measures the amount of oxygen in the exhaust gases and sends this information to the engine control module (ECM) or powertrain control module (PCM). The ECM/PCM uses this data to adjust the air-fuel mixture for optimal combustion.

When an O2 sensor malfunctions, it may provide incorrect readings to the ECM/PCM, causing it to miscalculate the air-fuel ratio. This can result in several issues, including sputtering.

Fix: Diagnose the issue with a diagnostic scan tool or OBDII scanner and replace the sensor. A faulty O2 scanner leaves codes P0150 -153.

Final Words

If your car sputters while accelerating, it’s likely a fuel injector or pump-related problem. However, a scan tool or OBD reader is the correct way to diagnose. It will lead you to the faulty components.

To address the issue independently, you can follow expert online tutorials. Nonetheless, as previously stated, many of these problems necessitate the assistance of a professional.

We hope this guide has provided valuable information on potential causes of sputtering in your car. By addressing these issues, you can enjoy a smooth and dependable driving experience!

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