16 Reasons Why Your Car Feels Sluggish

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Person driving a car on a mountain road

You’re driving along, and suddenly, your car starts to feel sluggish. It may be caused when you try to accelerate, or it just feels sluggish altogether. But what is the problem? Why is your car feeling this way?

If your vehicle feels sluggish it could either be a filter clogged up whether that’s fuel or air filter. Another culprit is a clogged catalytic converter which can make your vehicle feel sluggish when the gases don’t escape fast enough which slows down the combustion cycle. Also, Sensors like the o2 and MAF (mass air flow) sensors can affect the engine’s performance. Ignition coils and something wrong with the transmission may impact performance as well.

It’s always a good idea to start with the simplest things that are inexpensive and easy to replace checking to see after each step if there’s is a noticeable difference in the engine’s performance. The first I would recommend you do is scan for codes.

With an OBDII scan tool, check for what codes show up. That may help you pinpoint the issue quickly before you start going down the list. If you don’t have access to one I would highly recommend you pick one up like this BlueDriver. Also, any auto parts store can scan for codes free of charge.

16 Reasons Why Your Car Feels Sluggish

There are many reasons why your car feels sluggish. It can be something as simple as your air filter is clogged and needs to be cleaned out, or it could be something wrong with your transmission. Continue reading to figure out why your car is acting this way.

1. Air Filter Is Clogged

The clogged air filter is a common reason your car may feel like it isn’t running like it normally does. This is because no air is moving through and can cause congestion, like if you were to have a small cold and had trouble breathing.

Your engine needs clean air to be able to accelerate and run smoothly. The dirt and debris can also affect the combustion process of your vehicle. Oxygen is important to the combustion process.

It is always best to clean your air filter regularly to prevent this from occurring. Some people will remove the air filter and use the force of an air compressor to clean it. You can even purchase a new air filter. This is best if you have never replaced it before.

Mechanic opening up the housing where the car's air filter is stored with the air filter visible

2. Bad Fuel

Bad fuel can affect the combustion process of your vehicle and make your car run like it isn’t getting enough fuel. Usually, when you get bad fuel, it is because water has somehow gotten into the fuel tank. This can be either in your car’s fuel tank or simply bad fuel at the gas station.

When there is water in your fuel or bad fuel, your engine can’t burn the fuel as efficiently. This causes your engine to run poorly, making your vehicle feel sluggish. If you think water is in your tank, you can add Heet to help remove it.

Hand holding a fuel nozzle refueling at a gas station pump service station

3. Something With The Fuel System

Your fuel system can affect your engine and make it very sluggish. This doesn’t only include the fuel within your system (bad gas) but also other parts. Any malfunction in your fuel system makes it hard for your engine to produce power.

Some of the reasons why your fuel system isn’t performing correctly could be faulty components as listed below:

  • Faulty fuel filter
  • Sensor
  • Broken fuel pump
  • Fuel Injector
  • Fuel regulator
  • Leaking or clogged fuel lines.
  • Carburetor

Any of these can result in your car not running right. Although a simple fix, it can do a number on your car’s performance if ignored.

Car fuel filter
Old fuel filter

4. Spark Plugs Needs To Be Replaced

Spark plugs need to be replaced every so often. If they aren’t, they can get dirt and grime attached to it, which will impede your car from reaching its top performance. It will feel like your car bogs down as you are driving.

Spark plugs are an easy fix, and often you can tell if it is your spark plug by seeing if your car cuts out at top speeds. It should only take a few minutes to replace this part, and they are quite cheap to purchase.

Mechanic replacing the spark plugs on a vehicle with gloves on and the old spark plug dirty worn out in his hands

5. Low Compression

Compression is important for your engine to produce power. This happens when a leak or pressure is lost in the engine’s cylinders. There isn’t enough pressure to allow combustion, and your car becomes sluggish.

This is a more difficult problem to diagnose, which means you may not be able to fix this without professional help. It can cost a pretty penny, depending on where the leak is and how bad it is.

Auto mechanic using a compression gauge meter to measure the each cylinder compression on the car

6. Clogged Catalytic Converter

Your catalytic converter could be causing your car to be sluggish. When clogged, the airflow is disrupted and causes your car to run below its best performance. This is similar to if you are unable to let out all that carbon dioxide from your body. It would make you tired.

The exhaust system may not seem like it could do that much damage to your vehicle, but it can. Your engine isn’t getting enough air, and it will run slowly when you try to accelerate. It often feels like your car is “choking” when this is the cause.

If the catalytic converter is clogged your check engine light might come on if the o2 sensors are not faulty and actually detect an issue. Replacing it can be very expensive if you’re going with an OEM one. Aftermarket ones don’t have the same warranty standards and may not work with your specific vehicle. Removing it altogether and putting a straight pipe can impact performance and you might pass emissions too.

With all that being said there’s a solution you can try before going about replacing it. There are solutions you can add to your fuel tank when it’s almost empty specifically designed to help clean out the soot inside the catalytic converter. I would recommend trying something like Cataclean exhaust cleaner which is safe to use with any gasoline, diesel, hybrid, or flex-fuel car.

Cataclean 120007 Complete Engine, Fuel, and Exhaust System Cleaner, 473 Milliliter

Cataclean 120007 Complete Engine, Fuel and Exhaust System Cleaner, 473 Milliliter
Cataclean Fuel and Exhaust System Cleaner
Close up from the bottom of the car of the catalytic converter on the exhaust pipe

7. Sensors Are Malfunctioning

Sensors malfunctioning can often be the cause of why your car is not running correctly. Even with just one bad sensor, your car will run sluggishly. This is because your car is not getting the correct message from the sensor.

There are so many sensors. You can find them in every system in your car, so there are many places you can find a malfunctioned sensor. Here are a few places you can look:

  • Fuel system
  • Exhaust system
  • Ignition
  • Oxygen sensor
  • Engine Control Module
  • Mass airflow sensor

You can easily scan your car to see if a sensor is a problem. Technology has made it that much simpler to diagnose your car’s issues.

o2 oxygen sesnor close up on the exhaust pipe
Close-up of an o2 (oxygen sensor) on the exhaust

8. Damaged Or Loose Wires

Damaged or even loose wires can cause many problems with your engine. One damaged wire can make a system run incorrectly. This is because your engine cannot send the right messages to the right parts or sometimes provide enough power.

Damaged wires are an easy fix. You can replace them or just ensure they are attached correctly to a part. The only difficulty you will have with wires is finding the damaged or loose ones. It may take quite an investigation.

Check that the coil packs are nice and snug on the engine and check for any wiring going to any sensors mentioned previously to make sure there is no dirt or corrosion on them. It’s a good idea to spray electronic cleaner on the pins of the wiring plugs.

Close up of an automotive electrical wire that was chewed up and damaged destroyed by rodents

9. Faulty Ignition Coils

When your ignition coils become faulty, it can cause your car to move quite sluggishly. Your engine will not get enough power to continue driving safely, and you will need to pull to the side or find a place to park.

The ignition coil takes the electrical power and transforms it into a spark that can ignite the fuel. When it can’t do this correctly, your engine will not receive full power. You will need to get it replaced immediately.

Mechanic repairing ignition coils close up of one removed on a gasoline engine

10. The Alternator Or Alternator Belt

The alternator can be a reason for your car not running right. It helps keep your car running, so your car won’t run at full capacity when the alternator is faulty. It will seem like your car is running out of power. If your car shuts off completely, then your alternator is done for.

Sometimes it may not be your alternator but your alternator belt. If the belt is worn out or torn, it will affect the power that your car receives. You will thus have to replace it before the belt breaks completely.

Your belt may also have just slipped off and needs to be put back. This is a simple fix, and usually, you can see if this is the issue by opening the hood and looking at your alternator and the belts near it.

Close up of an alternator belt visible on a pickup truck engine

11. The Battery

The battery is a source of power for your car. When it doesn’t work like it is supposed to, your car will run improperly and could even stall. This isn’t always the case, but in severe cases, it does occur.

Your car needs electrical power to start and continue running. If it doesn’t, then you may find yourself without a running vehicle, and it could put a strain on other parts like the alternator. You don’t want that happening.

Replacing the battery is quick and easy. You can even have an auto parts store help you replace it by driving the vehicle there and buying a new one.

Auto mechanic testing the voltage on a car battery with a multi-meter

12. Bad Thermostat

A bad thermostat could allow your car to overheat. When the engine gets too hot, it can cause your car to run poorly. This is the same as if you were overheating during a hike. You get tired and can’t walk at normal speeds.

Your car cannot run properly when it is overheating. It can also cause further damage to other systems within your vehicle. Although this is a small fix, it could become an even bigger problem if left alone.

Mechanic removing the engine coolant thermostat from the vehicle

13. Bad Or Low Oil

Oil is needed to keep your engine running smoothly. When the oil goes bad, it can cause your engine to run slowly and seem like it is struggling to gain any power. It can also cause more damage to your transmission and the pistons within.

Low oil can also be harmful to your engine. When there isn’t enough oil, it is like your engine is anemic. Your car gets tired and can’t perform as it should. These are easy fixes with just a simple oil change or adding more oil.

Bad oil often looks dark and lacks any transparency. It could even look black on the dipstick. Oil usually has a bronze, transparent color. You should change the oil once it gets dark or even before then.

You should change your oil every 5 to 7,500 miles. You can do this yourself or get it done quickly at a local establishment. It shouldn’t take long, and you could even do it yourself if you wish to cut costs.

Oil dipstick and oil cap close up with oil levels good fluid check

14. The Transmission

Anything wrong with your transmission can cause your car to run badly. This may start as your car feeling sluggish or like it is being strangled from getting any power. If this persists without being fixed, it could ruin your transmission completely.

Many things contribute to your transmission running poorly. It could be a crack, leak, or just age. Without constant maintenance, your transmission becomes old, clogged, and worn out, making it hard for your vehicle to run correctly.

I would first scan for codes and confirm that there is indeed a possible issue with the transmission. Since transmission can get very pricey to fix or replace it’s best to confirm that the codes being pulled point to the transmission.

Check the transmission fluid to make sure it’s not extremely dark with fine particles in there. If there is that may be the issue and hopefully the only issue. If replacing the transmission fluids and filter doesn’t help, then there could be something wrong wither either a sensor, solenoids or the ECU/TCM that controls the transmission.

Bottom view of the transmission with the oil pan removed and the solenoids visible
Bottom view of the transmission on a car with the oil pan removed and the solenoids inside visible

15. The Timing Belt

Your timing belt may need to be replaced. It should be replaced about every one hundred thousand miles and done by a certified mechanic. It is crucial for the engine to maintain synchronicity while moving.

Your timing belt helps the pistons run and produce the energy needed to run correctly. When the pistons are out of sync, it can cause not only make your car run terribly, but it can cause damage to your transmission.

It is a small chunk of money to replace the timing belt, but it needs to be done. If you do not get these services completed, it can cost you a lot more than just a few hundred dollars. You may even have to buy a new vehicle.

Close up of an old cracked timing belt on an engine with the timing cover removed making the timing belt visible

16. Engine Control Module (ECM/ECU) or Transmission Control Module (TCM) Failure

The ECU and TCM are one of the most important parts of your vehicle. It helps monitor all the sensors to ensure that all systems are running properly and coherently. When this malfunctions, it is like driving blind.

Usually, when this first malfunctions, it will cause your check engine light to come on. But as you continue to drive your vehicle, it can disrupt many other systems and become dire to the extent of the damage to your car.

Some vehicles only have an ECU that controls both the engine and the transmission. Whereas other vehicles have a separate dedicated transmission control module. It all just depends on the year, make, and model.

Car engine control unit module ECU ECM installed in a vehicle with the harness plugs connected to it

How Do You Fix These Issues?

Many of these issues you can fix on your own if you are looking for a cheaper route. This includes cleaning your air filter or changing the spark plugs. Even changing a coil isn’t too difficult of a process, but there are many issues that need a mechanic.

The alternator, battery, and converter aren’t too difficult but are best completed by someone with some experience with fixing a car. You can do it on your own with some guidance. Depending on its position under the hood, the alternator may give you the most problem.

More severe issues like the timing belt, transmission, fuel system, and the computer itself should be completed by a professional. Replacing these parts is complicated and is best done by someone certified.

Ultimately, it is up to you if you hire a professional or work on the car yourself. Just do your research before settling on whatever route you choose and find a mechanic you can trust.

Mechanic changing the ignition coil on an engine of a car with blue gloves on

Conclusion

These may not be all the reasons for your car running sluggishly, but they are the most common. If you are unsure of the cause, you may want to go to a mechanic. They have all the tools necessary to check out your vehicle and find the root of this problem. Sometimes the issue can surprise you.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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