Dirty throttle body (Diagnosing and cleaning Guide)

Combustion engine based cars need two main elements in order to run: air and fuel. Whenever there’s a shortage of either element in the mix, the engine either stops functioning or lowers efficiency.

The throttle body acts like a gateway for fresh air to be drawn into the engine. However, the air outside is definitely not pure. Various particles can pass through the air filter and create deposits around the throttle body, causing irregularities when the engine is running.

Symptoms of a dirty throttle body

There are some obvious signs indicating a dirty throttle body and you don’t have to be a car mechanic to spot them.

First of all, the engine idle is a good place to start. Usually, when dirt deposits form around the throttle body, airflow into the engine either varies or becomes turbulent. This causes a particular imbalance within the combustion chamber and eventually leads to a fluctuating idle speed. Most cars idle between 700 and 1100 RPM.

However, the RPM needle should indicate a particular position on the gauge, and not swing between these values. If the car idles unevenly, it could indicate a dirty throttle body.

Secondly, when throttle bodies accumulate dirt, car acceleration diminishes considerably. To test this, one can get more aggressive on the throttle for a few times and check the result. If dirt actually blocks correct airflow towards the engine, the effect is better experienced when more air is needed – in this case, at acceleration rates. Here’s what happens; once you press the accelerator pedal, the engine will lag before actually start spinning faster. In more severe cases, heavy acceleration is no longer possible at all, and the engine shakes due to lack of fresh air.

A dirty throttle body may also cause lower mileage on a car. Since not enough air finds its way into the combustion chamber, the engine control unit (ECU) will tend to generate a rich mixture. In a rich mixture, more fuel is injected to compensate for the lack of oxygen. Since more fuel is injected, your car’s mileage will drop, using more gas for the same distances you used to travel with a clean throttle body.

Finally, lift the hood and have a look inside the housing. Generally, an uncommon amount of dirt deposits on the inner housing walls is a very good indicator of throttle body problems, thus requiring a thorough cleanup.

Throttle body cleaning guide

Once you have established that the throttle body is need of maintenance, it is time to get to work. Cleaning throttle bodies are an operation most car owners can do at home, as it doesn’t require very expensive tools.

In most cases, a throttle body cleaning operation requires:

  • Screwdrivers
  • Torx bits or socket wrenches (depending on the car)
  • A small brush (A toothbrush works great)
  • Protective glasses
  • A small flashlight
  • Throttle body cleaner (available in most auto shops)
  • Rubber gloves

To start off, make sure ignition is switched off and no electrical appliances such as headlights or radio are turned on. Next up, remove the ground (negative) terminal from your car’s battery. This is a safety prerequisite which will both ensure that you won’t cause a short-circuit during the cleaning process, but also that you won’t get electrocuted while doing it.

You may use your car’s manual to locate the throttle body. In most cases, the throttle body is located between the air intake system and the engine head. Most ducts and hoses are held together using clamps or metallic fasteners. Use the appropriate tools to remove them.

If you are having a hard time remembering positions, grab a bunch of masking tape to mark hoses and couplings as you disconnect them from the throttle body.

Furthermore, you may also take pictures of the area you’re working on after each hose or duct you are disconnecting. Use the photos as reference later on when you will reassemble the throttle body connections.

Make sure not to force any of the hoses leading to the throttle body. If you encounter increased resistance, stop the operation right away and ask for professional help. Broken or cracked hoses will cause vacuum leaks and affect engine performance even more.

On the other hand, if everything works properly, you should be able to uncover the throttle body. Now, the actual cleaning process begins.

Put on your rubber gloves and eye protection, then spray throttle body cleaner around the air duct. Spray in short bursts, allow a few seconds for the spray to penetrate dirt, then brush the residue and varnish with a small toothbrush or equivalent. Finally, use paper towels to wipe the dislodged residue. Repeat the entire process until the throttle body shines bare-metal.

While cleaning the throttle body, pay attention not to drop any parts or paper inside the throttle-body opening.

Once you’re done with the cleaning, reattached all the air hoses and ducts back into their original position and fasten them up properly. Reconnect the ground connector to the battery and start your car.

There is going to be an initial rumbles and uneven idling as the engine burns through the remaining cleaner fluid and incinerates any remaining varnish. Some white smoke may come out of the exhaust; however, it is completely normal and it will cease shortly.

Let your car idle for a few minutes, then hop in and take it for a test drive. The changes in engine responsiveness will be directly proportional to the amount of dirt that you had to remove from the throttle body. A really clogged throttle body will yield higher performance after being thoroughly cleaned while a less dirty throttle body may not provide too many changes after cleaning.

Nevertheless, you should regularly inspect your car’s throttle body in order to preserve the health of the engine, mileage and dynamic performance. In the same manner, make sure to regularly replace your car’s air filter to minimize dirt and varnish deposits.


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