9 Symptoms of a Bad or Failing Throttle Body : CARS24

9 Symptoms of a Bad or Failing Throttle Body

failing throttle Body

The throttle body is an important component in the air intake system of a modern car. Basically, it controls the volume of air that flows into the engine. This air is then responsible for the combustion. The right amount of air is important to be delivered to the engine for optimum combustion. So, in case of the throttle body malfunctions, the engine performance is directly impacted due to the incorrect volume of air entering the engine. Today, in this post, we take a look at the common symptoms that indicate a malfunctioning throttle body.

Vector diagram of Throttle Body

Source : SpectraPremium

Seen above is the vector diagram of a throttle body. The above image is a graphical representation of the flow of the air along with its pressure changes as it moves through the throttle body. It has an arrow (vector) that represents the directions of the flow of the air. Meanwhile, the length of the arrow shows the magnitude of the airflow. Other elements of the above diagram include vectors that represent the pressure and the velocity as well as represent the flow of air as it moves ahead in the throttle body. This is required for ensuring optimum performance and fuel mileage.

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Working of Throttle body

Source : Counterman

The throttle body is located between the air filter and the intake manifold. It contains a complicated throttle system that regularises the airflow, which is an essential part of the atomization process. It controls the air-fuel mixture ratio, thereby leading to optimum combustion. The basic controller for the throttle pressure is the throttle body temperature sensor that measures air-fuel ratio mixture that enters the fuel injection system. This regulation enables spark ignitions to offer the best fuel efficiency.  

The airflow is largely controlled by the throttle plate, which is also known as the butterfly valve. This valve is, in turn, controlled by the driver through the pressing of the accelerator. The accelerator’s pressing triggers a sensor on the throttle body which tells it to increase or decrease the air flowing into the combustion chamber. This increases or decreases the power output based on the input by the driver. 

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Symptoms of a Bad or Failing Throttle Body

failing throttle body

1. Grime buildup

A throttle body can easily get coagulated with dirt and grime. This build up is often referred to as ‘coking’ by technicians, and it results in an interrupted flow of air-fuel mixture. The flow of the working volume thus gets affected, resulting in an even idling. As dirt and grime accumulation further results in carbon deposition around walls of the throttle body, thereby disrupting the atomization air-fuel mixture. 

2. Electrical problems

Loose electrical connections can cause improper idling. Ineffectiveness of the signal transmission from throttle body to the car’s onboard computer can lead to faulty spark timings, improper injection of the fuel, and non-stoichiometric air-fuel mixture. These issues not only result in a bad idling, but can also switch the car into “limp-home” mode, restricting the power output from the engine, irrespective of the throttle input.

3. Airflow disruptions 

The throttle stop inside the throttle body works as a gate-keeper, helping the ECU understand if the throttle is open or closed. If it is not adjusted perfectly, it can cause the throttle position sensor to send wrong signals to the car’s computer. Consequently, an incorrect amount of air and fuel will be mixed together, which gives rise to symptoms like ill-timed spark and knocking.

4. Poor or high idle

Well, it is fairly easy to diagnose if your throttle body is in best shape or not by just observing the idle. A poor idling or high revs around idling are primary signs of an improper throttle body. If not checked in time, the issue can deteriorate the car’s health to a large extent. In fact, the engine’s life in the long run will also be hampered, due to this issue.

5. Worn-out Butterfly valve

The throttle body consists of a butterfly valve, which helps in regulating the air flow inside the combustion chamber. At times, even this valve can get in a bad shape, if dust, grime, and carbon particles accumulate in the throttle body. A worn-out butterfly valve results in improper throttle calibration and mis-aligned inputs.

6. The ominous check engine light

A check engine light is a big nightmare for a car owner. In case your throttle body goes for a toss in any way, the check engine light will show in the dashboard. After all, modern cars are equipped with electronic throttle control. It is, thus, easy for the on-board computer to detect the issue and inform the driver.

7. Lack of Power

If a throttle body fails to work properly, it results in making the mixture richer or leaner than required. A non-stoichiometric air-fuel mixture means that the car is either burning more fuel than required or less than that is needed for a perfect combustion stage. And, if a situation like this arises, the response from the accelerator pedal will not be ideal.

8. Issues while accelerating

Improper acceleration or stalling issues in a car can irritate the driver, and their existence in the long run can cause serious damage to the car engine. However, the presence of such issues also tells that a car’s throttle body has an underlying issue, and it affects the longevity of the engine.

9. Poor Mileage

A drop in the fuel mileage of a car is one of the biggest symptoms of a bad throttle body. One can measure the fuel economy or the mileage of his car using the tank-to-tank method. In this method, one needs to fill the tank to the full and note the odometer. Next, fill the tank as soon as it is about to get empty and take note of the odometer reading and the fuel that has been filled into the vehicle. Divide the distance covered between the two fuel stops by the amount of fuel that is filled the second time. THis will give you a fairly accurate mileage figure of the vehicle. In case the mileage of the car drops by over 15%, it could be a bad throttle body symptom. 


In order to ensure a smooth throttle body operation during the course of ownership of a car, there are a few things that one should take note of. Since the throttle body manages the air flow in the engine, the air filter should always be cleaned. In fact, the air filter should be changed as a part of scheduled preventive maintenance. Also, clean fuel should always be used in a car. Adulterated fuel can cause accumulation of dust and grime in the throttle body, as is the case with a worn-out air filter. To keep the throttle body clean, aerosol-based sprays can also be used. Keeping the water away from the engine bay too helps in preserving the wiring and electrical connections associated with the throttle body.


In case you experience any of the above signs in your car or if your car’s check engine light is blinking, you need to head to a trustable mechanic for a proper diagnosis. Also, it must be noted that spotting a malfunctioning throttle body is tougher than most other mechanical issues. So, in case you need to conserve the throttle body, you should consider using biofuel. Simply speaking, biofuel reduces the wear and tear in the throttle body. Also, regular tune-ups and proper maintenance can ensure long life of this vital component of the engine. 


Q. What is a throttle body?

A. In an internal combustion engine, the throttle body is a vital part of the air intake system which is responsible for regulating the amount of air that flows into an engine’s combustion chamber.

Q. What is the throttle body cleaning cost?

Throttle body cleaning cost could range anywhere between ₹350 to ₹500, depending on the type of vehicle. 

Q. Why is my car not speeding up? 

A car not speeding up or accelerating smoothly is one of the many symptoms of bad throttle body. 

Q. How do you know if the throttle body is bad?

There are many ways of recognizing a bad throttle body. Some common symptoms include fluctuations in RPM, poor performance and drop in fuel efficiency. 

Q. What happens when a throttle body goes bad?

A throttle body going bad means disturbance in the air-fuel ratio, which, in turn, leads to a drop in performance and mileage. 

Q. What causes a throttle body to go bad?

A common cause of the throttle body going bad is accumulation of dirt and grime.