Symptoms of a Bad or Failing Throttle Body

In today’s modern fuel injected cars, the throttle body is a critical piece of the air intake system that controls the amount of air flowing into the engine. The amount of air allowed in depends on how far the driver presses the accelerator pedal to the floor. As you press down on the pedal, the throttle position sensor receives a signal relative to where your foot is, ranging from all the way up (zero acceleration) to all the way down (full acceleration). This sensor relays the information to the car’s main computer — giving it constant updates as to the position of the throttle. The computer knows what to tell the fuel injection system in terms of how much more or less fuel to inject into the system based on the position of the pedal.

When this process is regulated properly, a perfect balance of air and fuel is introduced to your car’s engine, allowing it to run smoothly and perform at an optimum level. Here are 5 signs of a failing throttle body:

1.Grime Buildup

Dirt and grime can build up inside the housing, this being known as coking, and causing an interruption in air-fuel flow. As a result of not having an ordinarily smooth surface for the fuel and air to flow through, this delicate mixture is interrupted by a rough surface that causes an imbalance in the flow. Similar to dirt and grime, carbon deposits can create an uneven surface inside the walls of the throttle body, which can disrupt the atomization of the air-fuel mixture.

2. Electrical Problems

Electrical connection problems can cause inaccurate or intermittent information to be relayed to the car’s computer. As with any electrical connection, connectivity issues can cause a wide variety of unpredictable signals to be transmitted. In the case of the throttle body (and related sensor), when this happens it causes false information to be relayed to the car’s computer, resulting in faulty corrections to the air-fuel mixture. You may notice a switch into “limp-home” mode, where power to the car’s engine power is reduced and throttle operation is limited.

3. Airflow Disruptions from Vacuum Leaks or Throttle Stop

Vacuum leaks can disrupt the air-fuel flow because of an imbalanced airflow, which can cause throttle body pressure problems. The issue could also be an incorrectly adjusted throttle stop. This is a component that acts as a gate-keeper and establishes a minimum or maximum position for a throttle body plate to be opened or closed. A maladjusted stop wouldn’t allow in the correct amounts of air and fuel.

4. Poor or High Idle

When a throttle body is not functioning correctly, some noticeable characteristics may be poor or very low idle. This can include stalling when coming to a stop or very low idle after starting, or even stalling if the throttle is quickly pressed — resulting in the throttle body plate opening and closing very quickly.

In the case of a large vacuum leak, you may experience a very high idle because too much air is being allowed into the intake system. All of these symptoms will contribute to poor engine performance and, as a result, will cause your check engine light to come on.

5. Check engine light

The check engine light can indicate many issues within a car including a faulty throttle body. In more modern cars, an electronic throttle control (ETC) constantly monitors throttle body performance. Any problem detected with it will turn on the check engine light.

As a part of your regular service intervals, include the air induction service and fuel injection flush to clean out any carbon deposits and dirt. You will need to have the check engine light shut off by a qualified mechanic. This will include scanning your car’s computer system for fault codes to indicate problems with your fuel injection system and specifically throttle body components. These will give the mechanic an indicator as to what to check for and how to repair the problems.


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