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 is a function of how far the driver presses the accelerator pedal to the floor. As you press down on the pedal, a sensor called a 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 this information to the car’s main computer giving it constant updates as to the position of the throttle. The position of the pedal along this range is how the computer knows what to tell the fuel injection system in terms of how much more or less fuel to inject into the system.

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. There are a number of reasons that a throttle body may fail to work properly.

1. Dirt, grime, and carbon deposits on the inside of the housing

Dirt and grime can build up inside the housing, causing 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 with a rough surface which causes an imbalance in 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 inaccurate or intermittent information to be relayed to the car’s computer, resulting in faulty corrections to the air/fuel mixture.

3. Vacuum leaks or an incorrectly adjusted throttle stop

Vacuum leaks can disrupt the air/fuel flow due to an imbalance of air flow 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.

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

As a part of your regular service intervals, include the air induction service and fuel injection flush which cleans out any carbon deposits and dirt. You will need to have the Check Engine Light shut off by a qualified mechanic, such as one from [YourMechanic]. This will include scanning your car’s computer system for fault codes, which will likely 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.

This article originally appeared on as Symptoms of a Bad or Failing Throttle Body and was authored by Jeff Engstrom.

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