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Car Jerks When Stopped At Light – What To Do?

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Do you experience your car jerking while stopped? If you want to know what to do about this problem, then you’ve come to the right place. We researched this question thoroughly, and we have the answer for you.

One of the reasons why a vehicle would jerk while waiting at a red light is a dirty fuel injector. This can be fixed by a professional mechanic. Additionally, these issues can also cause an engine to jerk while it is at idle:

  • Weak battery or bad alternator
  • Worn spark plugs
  • Clogged air intake
  • Bad speed sensor
  • Bad mass airflow sensor
  • Engine vacuum

Learn about the other causes of car jerking while idle in the sections below. You will also learn the other symptoms of these different causes. Read on!

Traffic and car stopping at a traffic light, Car Jerks When Stopped At Light - What To Do?

How do I know if my fuel injectors are dirty?

A dirty fuel injector can cause your engine to get insufficient fuel. This leads to misfires, bucking, and jerking.

diesel engine injector

Here are some of the other symptoms of a dirty fuel injector:

Rough Idle

A rough idle can be caused by several problems. And dirty fuel injectors are one of them.

Your engine is rough idling when you notice that it is shaking and sputtering at traffic stops. A dirty fuel injector will cause the engine to get insufficient fuel, and this will cause it to shudder, struggling with what little fuel it has. This is often accompanied by an erratic RPM reading.

Issues With Fuel Economy

Dirty fuel injectors will cause you to have a bad fuel economy. Air and fuel are not mixed in the best ratio when you have dirty fuel injectors. This causes your car to have an erratic fuel consumption.

Dirty fuel injectors can cause your engine to consume too much or too little fuel. This creates a negative impact on your fuel economy numbers.

Poor Acceleration

Since you have an uneven fuel distribution, engine power will be affected as well. You will notice your vehicle having difficulty accelerating.

Can a bad battery or alternator cause your car to jerk?

Damaged and coroded car battery danger

If your car’s alternator can no longer provide the right amount of electrical energy for your vehicle to function correctly, then your car will try to get the rest of the electrical energy that it needs from the car battery. If the car battery cannot provide the missing electrical energy, then you can experience jerking from your car.

A low supply of electrical energy can negatively affect the spark plugs. The spark plugs are responsible for igniting the fuel and air mixture inside the combustion chamber. If the spark plugs are not getting the electrical energy that they need, they will not be able to perform their task, and the fuel and air mixture will not burn properly.

How do I know if I have a bad spark plug?

non-working chainsaw spark plug lies on an orange surface

As we discussed earlier, spark plugs are responsible for the combustion of the fuel and air mixture inside the engine. The valves inside the engine are filled with the right ratio of air and fuel. The piston will compress this mixture by moving upward.

The compression created by the piston increases the potential energy of the fuel-air mixture. Once the compression reaches its peak, the spark plug ignites the mixture to create an explosion that provides the engine the energy it needs to move your car.

If your spark plug has gone bad, the spark that it produces will become smaller and weaker. This leads to inefficient combustion of the fuel-air mixture that causes jerking.

Replacing the spark plugs should be done every 100,000 miles. It is also a good idea to replace the wiring of the spark plugs every other time that you replace your spark plugs.

How to tell if I have a clogged air intake?

Your engine needs the right amount of fuel and air in a compressed mixture to produce the right amount of energy for your car. Having a clogged air intake is like having a dirty fuel injector—it limits the amount of air that gets into the engine.

Thus, some of the symptoms of a clogged air intake are like the symptoms of a dirty fuel injector.

Additionally, you will notice the smell of gasoline inside your car. Since you get less air than what the engine needs to completely burn the fuel inside the combustion chamber, then you will have unburned fuel mixed with the exhaust fumes. This gives you the smell of gasoline inside your car.

The unburned fuel can create dark fumes going out of the exhaust pipe.

Check your air filter. If it looks dirty and there is a lot of debris on the air filter, then it is time to replace it. Dirt and debris on your air filter is the most common cause of clogged air intake.

The FRAM Extra Guard Air Filter for select Ford and Lincoln vehicles is available on Amazon. Check it out through this link.

How do I know if I have a bad speed sensor?

A speed sensor or a VSS (Vehicle Speed Sensor) is responsible for measuring the speed of your vehicle at the transmission level. This information is sent to the ECM (Engine Control Module). The ECM uses this information to determine the correct fuel-air ratio, the ignition timing, and the shifting point of the transmission.

The ECM depends on the accuracy of the information from the VSS to determine the fuel-air ratio and the ignition timing. If this data becomes unreliable, then the ECM will end up making the wrong fuel-air ratio and ignition timing. This results in jerking and several other problems with the engine.

Once the VSS starts to go bad, your vehicle’s automatic transmission will start to perform poorly. The automatic transmission will experience delayed shifting, limited operation of the gears, and hard shifting.

Another symptom of a failing VSS is an erratic movement of the speedometer, or the speedometer doesn’t provide a speed reading at all. Although you can still drive your car even with the absence of a speedometer, this will make it difficult to drive safely.

If your car has a cruise control function, a bad VSS will cause the cruise control to become inoperable. The cruise control is dependent on the data that comes from the VSS to function properly.

In most car models, a problem with the VSS will also trigger the Check Engine Light.

How to know if I have a bad mass airflow sensor?

Car air intake rubber duct with air sensor of engine

The MAF sensor or the mass airflow sensor is responsible for measuring the mass of the air that gets into the engine. This information goes to the ECM. The ECM uses the information to estimate the amount of fuel that is needed to match the amount of air.

A bad MAF sensor can no longer provide accurate information. The ECM will not be able to provide the correct ratio of fuel to match the amount of air that enters the engine if it doesn’t get the right information from the MAF sensor. The wrong ratio leads to jerking whether the car is idle or accelerating.

Some ECMs will severely limit the amount of fuel that they will inject into the engine if it determines that it is not getting reliable data from the MAF sensor. This can be a problem if you’re driving on the highway.

If the ECM hasn’t detected a problem with the MAF sensor yet and the MAF sensor has become too sensitive, the ECM will try to compensate by injecting too much fuel. This will cause a drop in the fuel efficiency of the car.

You will also notice that your car surges or hesitates during cruising or during acceleration. Fortunately, the MAF sensor is a part that you can replace yourself.

How to replace a faulty MAF sensor?

  1. Locate your MAF sensor. It is normally located close to the air filter box or the intake hose. It is characterized by having electrical wires connected to it.
  2. Carefully remove the electrical plug of the MAF sensor.
  3. Loosen the clamps and/or bolts on the air filter box to open it.
  4. Lift the box cover and set it aside. You might want to replace your air filter as well if it looks dirty. Replace the air filter only with the same type.
  5. Remove the old MAF sensor. Removing the MAF sensor is different for different car manufacturers and car models.
  6. If you want to try and clean the old MAF sensor, use only a MAF sensor cleaner. Other cleaners or liquids can leave a residue on the MAF sensor that can negatively impact its readings. Let the MAF sensor dry naturally after spraying it with the cleaner before inserting it back.
  7. If you decide to replace the old MAF sensor, simply slide in the new sensor.
  8. Reinstall the air filter cover.
  9. Tighten any fastening bolts and clips.

The CRC Mass Air Flow Sensor Cleaner is available on Amazon. Check it out through this link.

What causes car jerking only when idle?

If your car jerks only when idle, then there could be a leak in the engine vacuum. Have your car checked by a professional mechanic if this is the root cause of the problem.

Conclusion

Traffic and car stopping at a traffic light

There are several reasons why your car would jerk when stopped at a light. Know each of the different causes and learn how to eliminate the different causes.

If you enjoyed reading this article, you might find the articles below equally enjoyable to read:

Car Jerks When Shifting From Reverse To Drive—What To Do?

Why Is My Ford Fusion Jerking And Shaking?