8 Symptoms of a Bad Throttle Body (& Replacement Cost)

The throttle body controls the amount of air entering the engine. Here's how to tell if you have a bad throttle body

Throttle Body

The throttle body is an important mechanical component found in fuel-injected vehicles that control and regulates the amount of air flowing into the engine.

When the throttle body is in its appropriate condition, the engine receives an ideal air and fuel ratio and offers optimum performance. However, the combustion process will not occur properly when the throttle body is damaged due to an imperfect air/fuel mixture.

In this article, we will discuss the common symptoms of a bad throttle body, the location, and the replacement cost. Let’s begin with the signs to look for.

The most common symptom of a bad throttle body is a check engine light on the dashboard. You may also notice signs like rough idle, rough acceleration, or misfires during acceleration. High or low Idle RPM is also quite common when your throttle body is bad.

If you are still interested in more in-depth knowledge about each symptom, here is a more detailed list of the most common symptoms of a bad throttle body:

Bad Throttle Body Symptoms

1. Check Engine Light

Check Engine Light

The throttle body has some angle sensors and other sensors installed inside of it. As soon as the car’s onboard computer detects a problem with the throttle body signal, it will cause the check engine light to illuminate.

The check engine light also comes on due to several other reasons, which is why we recommend to visit an auto specialist and have the car scanned for any trouble codes when it pops up on your dashboard.

2. Rough Idling

Car Engine Rough Idle

If you notice your car’s engine idle is jumping up and down and make strange sounds, it may be due to a dirty or damaged throttle body.

The car engine is most sensitive at idle, where you will notice symptoms of a dirty or bad throttle body first.

3. Rough Acceleration

Slow Acceleration

The throttle body is also regulating the air-fuel mixture that is entering the engine. This means that a faulty throttle body can mess the air-fuel mixture up, which will cause problems when accelerating.

If you notice that your car has a very uneven acceleration – sometimes it is fast and sometimes slow, you might have a bad throttle body.

4. Misfires

Car Misfires

Misfires occur either when the air-fuel mixture is very wrong or when it comes to a weak spark from the spark plug. It is incomplete combustion inside the combustion chamber, in other words.

As we told you before, a bad throttle body can mess with the air-fuel mixture, and it can also cause your engine to misfire. Misfires are easiest recognized as small bumps when you are revving the engine.

5. High RPM Idle

High Idle Rpm

The throttle body controls the engine’s idle to make sure it is always holding a steady RPM. If there is a problem with the throttle body, it may cause the be way too high.

A not calibrated throttle body can also cause this. You can calibrate the throttle body with most diagnostic scanners.

6. Stalling Idle

Low Idle Rpm

The throttle body can affect the RPM the other way also. It can cause the RPM to be so low at idle so that the engine will die. This is often caused when there comes a lot of soot and dirt on the throttle body flap, which will cause less air entering the engine and therefore cause a low idle RPM.

Usually, a throttle body cleaning and a throttle body calibration with a diagnostic tool will solve this problem.

7. Poor Engine Performance

Slow Car

The engine requires both adequate air and fuel supply to perform effectively. If the engine is not receiving proper air supply due to a damaged throttle body, the engine will suffer, and as a result, the driver would experience a drop in performance.

If your car feels like it lost half of its power when accelerating, it can absolutely be caused by a bad throttle body.

8. Changed Fuel Consumption

Bad Fuel Consumption

You already know that a bad throttle body will cause a strange fuel mixture. This can also shop up on fuel consumption if you notice that you have to refuel more frequently or rarely; a bad throttle body could cause it.

Refueling less frequently might sound like a good thing, but your engine doesn’t think the same in the long run!

What Is a Throttle Body?

Volkswagen Throttle Body

The throttle body of your vehicle is basically a butterfly valve. The throttle body’s core function is to regulate and control the amount of air allowed to enter the engine.

The input data is sensed from the driver’s pressure on the accelerator pedal of the vehicle.

Consequently, more fuel is allowed to enter the internal combustion engine to ensure greater combustion and more acceleration power when more air enters the system.

There is only one throttle body in most vehicles, with a rare exception of special, larger vehicles. The function of the throttle body is also dependent on other parts, such as the air filter.

Cleaning the Throttle Body

Cleaning Throttle Body

Even if you have an air filter on your car, dirt and soot come from the turbocharger, EGR valve, and the crankcase ventilation and get stuck on the throttle body valve. After a whole, it will cover the valve so much that the RPM will be affected.

A dirty throttle body valve causes many problems with the throttle body; therefore, it is often possible to clean it. To find out more about cleaning it, you can check our guide here: Throttle body cleaning. Do not forget to recalculate the throttle body with a diagnostic scanner afterward, though.

Throttle Body Location

Throttle Body Location

The throttle body is most often located on the intake manifold at the big hose from the turbocharger or air filter.

Usually, aluminum is used for the manufacture of the throttle body. The location of the throttle body can be a little different for different vehicles.

However, according to the throttle body’s purpose, it should be located anywhere between the air filter and the intake manifold.

Throttle Body Replacement Cost

The average throttle body replacement cost is between $250 and $650, depending on the car model and labor costs. The throttle body cost between $200 and $500, while the labor cost is around $50 and $150.

The throttle body can be differently priced depending on different vehicles, models, and the manufacturing company. Basically, the main cost involved in replacing a throttle body is the cost of the parts required to be replaced.

Regular maintenance can effectively prolong the life of the throttle body’s parts, and you may not require a replacement for a long time.

The labor cost involved in the replacement can be economical or expensive, depending on which car shop you will for the replacement.

Remember that you need to make a recalculation of the throttle body valve after a replacement with a diagnostic scanner.

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Written by:

Magnus is the owner and main author of MechanicBase. He has been working as a mechanic for over 10 years, and the majority of them specialized in advanced diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.