Engine misfiring or stumbling is a sign that your car is not getting enough power from the engine during acceleration. A car sputters when accelerating due to the fact air and fuel is not being properly mixed, therefore, forcing the car to run on unburned fuel. Another reason could be a weak transmission system that misfires when the engine experiences an extra load. A normal car reaction would be to open up the throttle upon acceleration so that the right amount of air can get in and mix with fuel for a seamless acceleration.


What are the probable causes of engine hesitation?​

  • Dirty or clogged fuel injectors​
  • Bad or malfunctioning MAP sensors
  • Dirty mass airflow sensor
  • Leakages
  • Contaminated fuel
  • Low fuel pressure as a result of a leaking fuel pump or regulator

An engine hesitation should not be confused with an engine misfire because hesitation normally occurs when accelerating while a misfire can take place anytime due to the following reasons:

  • Faulty or Wet plug wires
  • Bad ignition coil
  • Worn out or dirty spark plugs​

Diagnosing the Problem

There are many ways or tools that you can use to try and understand why your car sputters when accelerating:

  • Making use of a scan tool that can read the vehicle’s fault codes and fuel trim readings
  • Checking the response rate of the various sensors
  • Visually inspecting for leaks when the car is in idle mode​

Troubleshooting Car Sputters

This is a step by guide for any car DIY enthusiast who knows one or two things about the basic functioning of an engine. This article can be used as a reference when dealing with any type of car or engine.

What You Will Need​

  • Protective gloves and eye goggles
  • Scanner for code reading
  • Carburetor Spray
  • Screwdriver
  • Flashlight

NOTE: Park the vehicle on a level ground and make sure that the car is in park mode and the emergency brake is engaged. You may have to keep the engine running to get the most accurate results from some of the tests to be carried out.

Step #1: Read the Engine Codes​

Use the scan code reader to read and diagnose to see what repair needs to be done. You can use a reliable scanner that is able to read and troubleshoot the codes.

Step #1: Read the Engine Codes​

Step #2: Check the Fuel Filter​

You can remove the fuel filter and physically test the flow of liquid by blowing through it. A good filter should be able to have a smooth flow when air pressure passes through it. Poor fuel pressure will force the engine to run on lean fuel causing the sputter.

Step #2: Check the Fuel Filter​

Step #3: Check for Leaks​

A leaking engine will send wrong data to the electronic control unit (ECU) forcing the car to sputter because of the existing vacuum created by air in the oil. If you can spot any damage to pipes or vacuum lines, you can repair or replace the pipes.​

Step #4: Check the Fuel Pressure​

You can use a fuel pressure gauge to get the exact readings of the fuel pressure. Poor or low pressure is what is causing the vehicle to stumble when trying to accelerate. Some vehicles have a built-in fuel pressure gauge that automatically increases the pressure when the accelerator is depressed. This will respond according to the size of the load the car is carrying to improve efficiency. Some cars have their pressure regulator located on the fuel rail.

Step #4: Check the Fuel Pressure​

Step #5: Check the Mass Airflow Sensor​

Any leakages that can be detected by the air flow sensor should be fixed. Look for tear and wear on the intake boot and replace if necessary. The sensor is supposed to relay information back to the ECU for analysis if there is a leak the vehicle will have a problem accelerating.

Step #6: Check the Mass Airflow Sensor Components​

Sometimes the external parts of the mass air flow may not be having the problem. When you look at the device, you will see a hot wire which may be contaminated when it comes into contact with air and debris. It is recommended that you replace the hot wire after every 70,000 plus miles.

Step #7: Look at the Throttle Bore​

Its main work is to control the volume of air getting into the engine. Due to its position in the engine, the throttle bore attracts dust and debris and it must be cleaned to return the engine back to its optimal performance.

Step #7: Look at the Throttle Bore​

Step #8: Check the Spark Plugs​

Spark plugs ignite the air-fuel mixture while inside the combustion chamber to power the engine. Worn out or misaligned spark plugs will give wrong ignition timing and lead to engine hesitation. If you suspect they are the issue, replace or re-align them.

Step #8: Check the Spark Plugs​

Step #9: Check the Clutch​

A worn out clutch will not successfully release the engine from the transmission, this is what causes hesitation every time you want to accelerate or change the gears. If you see any sign of wear and tear on a clutch, replace.

Step #10: Look at the Timing Belt​

This is an important component that connects the crankshaft and the camshaft. The alignment has to be perfect for the car to pick speed upon acceleration. Look for any damages or wear on every inch of the belt. A bad timing belt should be replaced by a matching type and size.

Step #11: Check the Harmonic Balancer​

This is a device that is connected to the engine’s crankshaft built to reduce harmonic vibrations from the crankshaft. These vibrations if not checked are capable of reducing your car speed. Look at the keys of the balancer and see if there is any hesitation on their movement.


Fixing car engine hesitation depends on the exact problem that is directly related to your car sputters when accelerating. If you have gone through all the steps and still not able to get a solution, it is recommended that you take your car to the nearest and a trusted auto mechanic to complete the diagnosis. There are several reasons that can cause a car not to pick up when accelerating, it is our hope that this blog post has opened up your eyes on all the possible cause and probably how you can handle them.

Please share the article and remind your friends that all parts that need to be replaced must be bought from trusted dealers!

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Chief editor at Paul's Gigantic Garage. I came up with this blog to help you to sort out some basic problems your car may be facing and in turn, save lots of cash by some of my DIY tips that I hope will get your car out of its current situation. I also had in mind motor enthusiasts who for the love of cars who are constantly looking for information about cars on the latest trends, questions, fixes, driving, tricks, and accessories.


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