Car Won’t Maintain Speed? 4 Most-Common Issues (Solved)

Encountering problems with your car failing to maintain speed? This is a common concern for many drivers.

In this article, we delve into the causes and provide practical solutions to put you back in control.

Let’s explore together.

Clogged Air Filter

A clogged air filter can significantly impact a car’s ability to maintain speed. The air filter’s primary function is to trap dirt, debris, and impurities, preventing them from entering the combustion chamber. An engine requires a balanced air-fuel mixture for optimal performance, and restricted airflow can disrupt this balance.

When an air filter becomes clogged, it starves the engine of much-needed air, leading to poor acceleration and difficulty maintaining speed.

In some cases, replacing a dirty air filter can improve acceleration or horsepower by up to 11%.

Symptoms of a clogged air filter include erratic idling, reduced fuel efficiency, and lackluster acceleration. To inspect the air filter, start by locating it within the engine bay, typically inside a rectangular plastic housing.

Open the housing and visually inspect the filter.

A clean filter should appear white or light gray, whereas a dirty filter will be darker, with visible debris and dirt buildup.

If the air filter appears dirty or clogged, it’s essential to replace it promptly to prevent further performance issues and potential engine damage. Car owners can easily replace their air filters with some basic tools, following the car manufacturer’s recommendations.

Some factors contribute to air filter clogs, such as driving in dusty or polluted environments, frequent short trips, and even the age of the vehicle.

To avoid clogged air filters, it’s crucial to follow the vehicle’s maintenance schedule and replace the air filter as needed.

Faulty Throttle Position Sensor

A faulty throttle position sensor (TPS) can cause a car to have difficulty maintaining its speed. The TPS is a critical component that monitors the position of the throttle valve, which regulates the engine’s air and fuel mixture.

When the sensor malfunctions, it can send erratic signals to the engine control module (ECM), leading to various issues.

Some common symptoms of a bad throttle position sensor include:

  • Slow or hesitant acceleration
  • Stalling, especially at low speeds or when idling
  • Increased fuel consumption
  • Rough or erratic idling
  • Difficulty switching gears

If the check engine light comes on, it could indicate a problem with the TPS. In addition to the light, drivers may experience loss of power and an inability to accelerate beyond a certain speed. To diagnose and reset a TPS, an OBD2 scanner can be used, provided it is compatible with the specific car model and has a throttle sensor reset feature.

When replacement of the throttle position sensor is necessary, it is important to choose a high-quality, compatible part. A professional mechanic can advise on the optimal choice and perform the replacement safely and efficiently.

Malfunctioning Mass Airflow Sensor

A malfunctioning mass airflow (MAF) sensor can cause a car to struggle to maintain speed. The MAF sensor measures the amount of air entering the engine, providing data that helps calculate the appropriate air-fuel mixture for optimal combustion.

When the sensor fails or sends inaccurate information, the engine’s performance can be compromised.

Symptoms of a bad MAF sensor include poor drivability, engine stalling, jerking or hesitation during acceleration, rough or jerky acceleration, and poor fuel economy. The car engine may “starve” due to a lean air-fuel mixture, causing it to jerk and struggle to maintain speed.

There are several methods to diagnose and fix a malfunctioning MAF sensor. One option is to use an MAF sensor-specific cleaner to remove any contamination or debris that may be affecting the sensor’s performance.

Thoroughly cleaning the intake tubing and replacing the air filter can also help prevent future dust intrusion.

Another method is to have the MAF sensor tested by a professional mechanic. Using diagnostic tools, the mechanic will assess the sensor’s functionality and determine if it should be replaced.

It is important to note that a failing MAF sensor can occasionally trigger the check engine light or create diagnostic trouble codes, making it easier to identify the issue.

Worn Out Spark Plugs

Worn out spark plugs can significantly impact a car’s ability to maintain speed. When spark plugs become worn or fouled, they lose their efficiency, leading to decreased engine performance.

Drivers may experience sluggish acceleration, reduced fuel efficiency, and a lack of responsiveness while attempting to maintain or increase speed.

There are several symptoms to recognize in vehicles with problematic spark plugs. For instance, a noticeable decline in the car’s acceleration capabilities may occur. Acceleration may feel slower than usual, or the car might struggle to reach or maintain its desired speed.

This issue stems from the engine’s inability to fire efficiently, resulting in reduced power output.

Another symptom is an increase in fuel consumption. Cars with improperly functioning spark plugs struggle to burn fuel efficiently, leading to worse gas mileage. This can add up to increased expenses for the owner and a less eco-friendly vehicle.

To prevent issues related to worn out spark plugs, car owners should consult their vehicle’s owner’s manual to determine the appropriate replacement interval. Replacing spark plugs in a timely manner ensures optimal engine performance and the ability to maintain consistent speed on the road.

Car Systems And Components To Check

Using A Diagnostic Code Scanner

A diagnostic code scanner can help identify issues related to the engine control module (ECM) and other electronic components.

Plug the scanner into the vehicle’s on-board diagnostic system (OBD-II) port under the dashboard and read the trouble codes that appear.

Fuel System

The fuel system consists of the fuel pump, fuel filter, fuel injectors, and fuel pressure regulator. These components work together to deliver fuel to the engine.

Check for clogged fuel filters, defective fuel pumps, or dirty fuel injectors that may prevent the engine from maintaining speed.

  • Fuel Filter: A clogged fuel filter restricts the flow of fuel to the engine, causing performance issues.
  • Fuel Pump: A failing fuel pump may not deliver enough fuel to the engine, leading to insufficient power.
  • Fuel Injectors: Dirty or malfunctioning fuel injectors can cause poor acceleration and difficulty maintaining speed.

Ignition System

The ignition system is responsible for creating and distributing the electrical spark required for combustion. Components to check include:

  • Spark Plugs: Worn or fouled spark plugs can lead to weak combustion and difficulty maintaining speed.
  • Ignition Coils: Failing ignition coils can cause weak or inconsistent sparks, resulting in poor engine performance.
  • Ignition Timing: Incorrect ignition timing can lead to slow acceleration and difficulty maintaining engine speed.


The transmission is responsible for converting the engine’s power into movement. Problems with the transmission may cause the car to struggle to maintain speed. Check for:

  • Transmission Fluid: Low or dirty transmission fluid can cause shifting issues and reduced engine power.
  • Transmission Speed Sensors: Malfunctioning speed sensors can result in incorrect gear shifts, leading to difficulty maintaining speed.
  • Shift Solenoids: Faulty shift solenoids can cause delayed or erratic gear shifts, impairing the vehicle’s ability to maintain a consistent speed.

Fixing The Issue

A common cause for a car not maintaining speed is a clogged air filter. To resolve this, ensure the air filter is clean and there are no obstructions preventing airflow. Replace the filter if it appears to be dirty or damaged.

Another reason could be a malfunctioning mass airflow sensor that incorrectly measures the air entering the engine, leading to a lean air-fuel mixture. Inspect the sensor for dirt or damage and clean it if necessary. If the problem persists, consider replacing the sensor.

Transmission issues may also affect a car’s ability to maintain speed. Check the transmission fluid levels using the dipstick, making sure the fluid is at the correct level and appears to be in good condition. If the fluid is low or discolored, consider changing it or consulting a mechanic for further assistance.

A worn clutch can lead to difficulty accelerating and maintaining a constant speed. Inspect the clutch for wear and consider replacing it if it’s damaged or slipping. Additionally, a faulty sensor may affect the car’s performance. Utilize an OBD2 scanner to identify any fault codes and consult a mechanic for guidance.

Remember, when addressing these issues, always adhere to the car’s owner’s manual for specific instructions on maintenance and repair procedures. It’s essential to use the recommended replacement parts and fluids to ensure optimal performance and safety.


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