6 telltale signs of a dirty air filter that will tell you it's time to clean or replace

The air filter is an essential component of your car’s intake system. Its job is to prevent contaminants from the air entering the engine and causing damage to internal components.

Over time, the filter will collect dust particles from the air and will gradually become dirty and clogged. After a few miles of normal driving, the air filter might become clogged from too much dirt, creating an obstruction to the intake of air.

An internal combustion engine needs to maintain an ideal air-fuel mixture of 14.7 parts air to 1 part fuel for optimal performance. In this process, the air filter is essential for delivering clean air to the engine.

However, when a dirty air filter hampers airflow and supplies less fresh air than what the stoichiometric ratio calls for, it can lead to an oxygen-deprived engine, resulting in a fuel-rich mixture that doesn’t burn efficiently.

In modern engines equipped with either a MAP or MAF sensor, this issue might be experienced as a loss of power. Meanwhile, in older systems, an excessively rich air/fuel mixture causes by bad air filter can trigger the vehicle to surge, sputter, or even stall.

Thus, being aware of common symptoms associated with a dirty or clogged engine air filter is crucial for determining when it requires cleaning or replacement.

Luckily, cleaning or replacing a contaminated air filter is one of the easiest tasks you can perform on your vehicle. In fact, it’s the perfect job to get started in the world of automotive mechanics if you have never done it before.

Read on to learn more about the telltale signs of a dirty engine air filter, the consequences of neglecting it, and how to get your engine breathing fresh air again.

What Does an Engine Air Filter Do?

What Does an Engine Air Filter Do?

The air filter has the important job of preventing contaminants from the air getting into the engine. The engine works with very small and tight tolerances, and any debris can cause damage or accelerate wear to internal components.

An engine uses oxygen and fuel to create combustion, which provides the energy to move the car. This oxygen is aspirated from the exterior in the form of atmospheric air via an induction or intake system. Upstream of this piping sits the air filter. Therefore, it plays a very important role in ensuring the longevity and reliability of your engine.

6 Telltale Signs Your Car Air Filter Is Dirty and It Needs Cleaning or Replacement

In modern engines with sophisticated computer control, there’s usually very little to tip you off that the air filter might be getting clogged. In older systems with more rudimentary control systems, however, the lower intake of fresh air will throw off the fuel injection system, causing a lot of problems to rear their ugly head. Here are the six symptoms that indicate your air filter is clogged or dirty, and it may be time to clean or replace it:

1. Reduced engine power

Reduced engine power

A slow and sluggish driving performance, including jerking when accelerating or delayed response, can be a key indicator of restricted airflow into your engine. This issue often stems from a clogged air filter, which prevents the optimal amount of air from entering the engine. Consequently, less fuel can be injected, and the ideal air/fuel ratio cannot be maintained. As a result, there is a decrease in the power output produced.

You might notice that you need more accelerator input to maintain the same speed on the highway, for example. If you feel the engine doesn’t pull as hard as it used to, it’s a good idea to check your air filter before you go jumping to more expensive conclusions.

2. Check engine light

Check Engine Light

On engines with electronic fuel injection, the filter is located upstream of the MAF or MAP sensor. These sensors read the actual airflow into the engine. The ECU then takes this information into account when deciding the amount of fuel to inject in order to maintain the optimal 14.7-to-one air/fuel ratio.

Based on the throttle position and the input from other sensors, your ECU may be tipped off to the fact that less air is being drawn into the engine than it should, triggering an error. As a result, you might get a check engine light to let you know that something is wrong.

3. Increased intake manifold vacuum

Increased intake manifold vacuum

If you have a boost gauge from the factory, you might notice the needle is pointing lower toward maximum vacuum at idle. That’s because the engine must work harder to suck in air through the filter element in order to overcome the obstruction, creating a bigger pressure differential across the throttle valve.

4. Engine misfires

Engine Misfires

When an air filter is severely clogged, the airflow to the engine could theoretically be limited to such an extent that the ECU cannot compensate enough or that stable combustion cannot be sustained anymore. This can cause an excessively rich air-fuel mixture that cannot ignite, leading to engine flooding and carbon-fouled spark plugs. As a result, you may experience difficulties starting the engine or notice misfires.

Although it would need a really dirty filter to reach this point, you would start getting unburned fuel in the cylinders. This would lead to a lot of problems, such as fouled spark plugs, misfires, sputtering, backfires, or damaged catalytic converters.

5. A dirty-looking filter

A dirty-looking filter

This might sound obvious, but a good way to spot a dirty air filter is simply to look at it. A brand-new filter is usually a very light color, generally white or light yellow. The filter will gradually turn a darker color as it absorbs smaller fine dirt particles.

A visual inspection will reveal the state of the filter: if it is a very dark color, it means it probably could use a clean-up or replacement.

6. Other issues with older engines

Other issues with older engines

In older cars with carburetors or fuel injection without closed-loop lambda control, the engine may be unable to compensate for the lack of air. This makes these engines much more susceptible to problems stemming from a dirty air filter.

The excess fuel could cause the mixture to turn rich, which causes the formation of unburned hydrocarbons that can lead to several issues, such as:

  • fouled spark plugs
  • difficulty starting the car
  • strange engine noises
  • rough idle
  • misfires
  • strong gasoline smell, especially after starting the engine
  • black smoke coming out of the exhaust
  • notable decrease in fuel economy

Should You Clean the Air Filter or Replace It?

Should You Clean the Air Filter or Replace It?

Cleaning non-reusable filters is not advisable. While it may temporarily improve the filter’s performance, it’s highly unlikely that you will be able to clean it thoroughly, leaving dirt particles embedded in the filter element, which will still cause an obstruction. Therefore, you should always replace them completely.

Furthermore, these filters are normally made of paper. They are very fragile, so any attempt to clean them might damage the filter, which will significantly reduce its ability to catch contaminants from the air properly.

Washable filters, on the other hand, are meant to be purchased only once and then last the lifetime of the vehicle. Normally you will also need to buy a kit with cleaning and oiling solutions for these filters, which adds some expense to their overall cost.

When To Replace an Air Filter?

Check your car manufacturer’s recommendations to see how often you should replace your air filter. Normally, this will be every 15,000 miles or every two years or so but it can be less if you live in a very dusty area. You should also replace the filter when it is visibly clogged or dirty, as that will adversely affect the performance of your engine.

How to Clean or Replace an Air Filter

Cleaning or replacing your air filter is a very basic job that, in most cases, can be done without any tools. Here’s the step-by-step guide:

  1. Locate the airbox on your vehicle – In most modern cars, this will be a black square plastic enclosure that sits close to the front of the car, to one of the sides. If you have an older carbureted car, the filter will be close to the engine intake and can take a circular or conical shape.
  2. Open the air filter housing This will normally be held in place only by a few clips. Be careful not to break any of them in the process, as this can cause rattling noises down the road. Occasionally the airbox lid can be fastened with Phillips head screws instead.
  3. Remove the air filter Take great care not to let any debris or dirt fall into the intake piping. Cover the airbox with a clean rag to avoid any debris falling in if the filter is going to be removed for a long period of time (e.g., for cleaning and drying).
  4. Skip this step if you are installing a brand-new replacement filter If you have a reusable filter, clean it carefully with a solution of water and cleaning product, and rinse thoroughly under a faucet or with a garden hose until it appears clean. Be careful not to stretch or tear the filter. Use compressed air to dry it out, or leave it out in the sun for a few hours. Apply a coat of oiling product after you’re done.
  5. Place the air filter back into place and close the housing.

Engine Air Filter Replacement Cost

Engine Air Filter Replacement Cost

A non-reusable air filter is a pretty cheap part, with most new filters from reputable companies costing 10 to 30 dollars. If you opt to go with a cleanable filter, it will set you back around 50 dollars for the filter, plus another 20 dollars or so for the cleaning and oiling kit.

If you have a repair shop do the work for you, you might have to pay an additional 20 to 50 dollars in labor costs. So, it definitely pays to do the work yourself.

Frequently Asked Questions

What happens when the air filter is too dirty?

When the air filter gets too dirty, it creates an obstruction, causing the engine to breathe in less air than it is supposed to. In modern engines with close-loop lambda control and MAF/MAP sensors, the main symptom of a dirty air filter is a lack of engine power due to the smaller amounts of air entering the engine.

That’s because the ECU can compensate for the lack of air with a corresponding decrease in fuel. If your car features an older engine design with more archaic control systems, you may experience a host of engine problems like difficulties starting the car, a rough idle, misfires, reduced fuel economy or a strong gasoline smell.

Is it better to have no air filter or a dirty one?

That depends on what you mean by “better”. From a reliability standpoint, having no air filter is definitely not recommended. While the engine will be able to breathe easier, it will also be able to swallow a lot of impurities which can cause internal damage.

Big dirt particles can damage valve seats, piston rings, or score the cylinder liners, leading to very expensive repairs. In the end, it’s better to have a new, clean filter.

From a performance point of view, no air filter provides far less obstruction to the airflow than a clogged filter and may increase maximum engine power. That’s why performance tuning often comes in the form of custom air filter elements which offer lower filtration capability, and race cars go as far as not to have any air filters at all.

However, such racing engines are designed to be rebuilt often and not go for 200,000 miles or more with little maintenance like a normal street car.

Can I replace the air filter myself?

Yes, you can definitely replace your engine air filter yourself. This is the ideal job to get you started in the world of car maintenance since it’s very easy to do, and there’s very little potential for things to go horribly wrong due to a lack of experience. All you will need is a replacement air filter and, potentially, a Phillips screwdriver.

Victor Faeda

Written By

Victor Faeda

Victor is a Mechanical Engineer BSc and certified Automotive Mechatronics technician from Portugal. He worked as an intern mechanic for Volvo and has been fixing his own vehicles for over 10 years. Writing and cars are his passion, so now he combines the two by creating content around the automotive industry. He specializes in automotive technology and maintenance.

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