Symptoms of a Bad or Failing Throttle Body

Modern electronic fuel-injection systems are some of the most easily-maintained systems in your vehicle, and rarely experience problems. But, once your vehicle has accumulated more than 75,000 miles, the system will need to be tuned up.

The two most common maintenance jobs for this system are fuel-injector cleaning and throttle-body cleaning. In this article, we’ll take a deep dive into the throttle body– and what happens when things go wrong.

The Science Behind the Part

The throttle body is a critical piece of the air intake system. That controls the amount of air flowing into the engine.  As the driver presses down on the accelerator pedal, the throttle position sensor receives a signal telling it 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 — providing constant updates about the throttle position. The computer takes in all the information and knows how to adjust the fuel injection system, providing more or less fuel based on the position of the pedal.

Signs and Symptoms of a Problem

If your car runs rough when idling, the cause just might be a dirty throttle body. Once you look inside a throttle body, you will probably be surprised at the dirt, gum and varnish that have accumulated there over time. The throttle body controls the amount of air the engine takes in, and when it gets dirty, the engine can’t idle smoothly. As the vapors bake from the engine heat, they form black sooty carbon deposits inside the throttle body. Here are the most common signs a failing throttle body we’ve seen in our shop:

1. Grime buildup
Dirt and grime can build up inside the part’s housing (some mechanics call this “coking”) causing an interruption in air-fuel flow. This causes the delicate mixture of air and fuel entering the system to be interrupted by a rough surface– causing an imbalance in the flow. Similar to dirt and grime, carbon deposits can also create an uneven surface inside the walls of the throttle body, which disrupts 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. In the case of the throttle body (and related sensor), delayed to false information can cause the computer to make faulty corrections to the air-fuel mixture. You might notice a switch into “limp-home” mode, where the power to the car’s engine noticeably reduced power is reduced no matter how hard you press the pedal.

3. Airflow disruptions 
A poorly adjusted throttle stop can also cause an imbalanced airflow which, in turn, can cause throttle body pressure problems. The throttle stop serves as a gate-keeper, and helps the computer detect when the throttle body plate is “opened” or “closed.” If not properly positioned, the stop can leak or get stuck preventing the correct amounts of air and fuel from flowing.

4. Poor or high idle
When a throttle body is not functioning correctly, you’ll usually notice a distinctly poor or very low idle. If the problem is really severe, you might even begin stalling when coming to a stop or when the throttle is quickly pressed. This will inevitably contribute to poor engine performance and, if it gets to that point, it should cause your check engine light to come on.

5. The ominous check engine light.
In more modern cars, an electronic throttle control (ETC) constantly monitors throttle body performance. If the system detects a problem it will turn on the check engine light.

While throttle-body cleaning is good preventative car maintenance, it will also help engine drivability. 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.

At V&F

Recommended maintenance may not seem like a big deal, especially if your car seems to be running fine. But it’s not something vehicle owners should ignore. Knowing the typical lifespan of each part they use, manufacturers can estimate these breaking points and recommend usage-based check-ups to help ensure vehicle performance and reliability. Keeping up with factory-recommended maintenance helps extend the life of your vehicle and can prevent high-cost repairs in the future.

In fact, if you’ve noticed a rough idle, stumbling initial acceleration or even stalling – all when the engine is fully warmed up – a dirty throttle body could be the culprit. V&F offers regular Factory Scheduled Maintenance, including 30/60/90/120K Mile Services where applicable, to ensure optimal vehicle health. If your car is in need of scheduled maintenance, give us a call or make an appointment online.

Written by Nicole Palange

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