Bad Throttle Position Sensor Symptoms

Your car has dozens of sensors onboard—one of which is the throttle position sensor (TP). As you might have guessed, the TP sensor measures the position of the throttle blade.

Older vehicles have just one TP sensor, whereas newer models with electronic throttle control (ECT) have two sensors as a fail-safe measure.

Although the TP sensor is a relatively simple part, it can cause several noticeable symptoms if it fails.

What Is A Throttle Position Sensor?

The throttle position sensor monitors how far open the throttle valve (or blade) is open, which is determined by how far down the accelerator pedal has been pushed.

The throttle position controls the amount of air that flows into an engine’s intake manifold; when it’s opened wide more air flows in; when it’s nearly closed, little air flows in.

The position of the throttle and how quickly it’s opening or closing is transmitted to the engine control module, and that information is among the factors the computer uses to decide how much fuel is injected into the engine and the spark timing. The TPS is usually mounted on the throttle body (the housing that contains the throttle valve).

When a TPS malfunctions it can trigger a “check engine” warning light or cause the engine to idle roughly, surge, hesitate or stall because the engine control module doesn’t know what the throttle position is and can’t correctly set the fuel mixture or ignition timing.

Symptoms Of A Bad Throttle Position Sensor

Symptoms Of a Bad Throttle Position Sensor

So, how do you know when you have a failing throttle position sensor? Here are some of the most common symptoms of a bad sensor.

#1. Rough Idling.

As your car idles, there should be relatively little movement in the position of the throttle. It should be slightly open, allowing in just enough air to keep the car running at an idle. However, a bad sensor might cause some wobbling in the position of the throttle.

Instead of remaining still, it might open and close a small amount instead. This will cause the engine RPMs to waver instead of remaining steady. If you notice that your vehicle is idling rough, then your TPS might be to blame.

#2. Check Engine Light Illuminated.

A check engine light can signal many different problems, and a bad TPS is one of those problems. Since the TPS on your vehicle controls the amount of air that enters your intake manifold, a bad sensor allows either too much or too little air.

There are other sensors in the vehicle, like the mass airflow sensor, that also measure air readings. When the readings are outside the normal range, this will cause your check engine light to illuminate.

You should have an automotive repair shop read the trouble codes from your ECU with a scan tool to determine whether your TPS is the cause of the warning light.

#3. Frequent Engine Stalling.

This is one of the symptoms that can make your car dangerous to drive. If your TPS causes the butterfly valve in your throttle to close too much while driving, then it will cause your car engine to die.

A malfunctioning TPS can also affect your car’s fuel injection system. It might not deliver enough fuel into the engine, and this can cause your vehicle to stall as well.

If this situation happens frequently, then you should have a mechanic check your vehicle to determine whether your TPS sensor might be the issue.

#4. Poor Fuel Economy.

Since your throttle body sensor has a direct relationship with the air/fuel ratio in your engine, a bad sensor can cause your car to burn excess fuel. When the sensor is in the wrong position, your fuel pump might be pumping too much fuel through the injectors.

Even though the vehicle does not need this much fuel, the computer believes that it does because it is receiving a faulty reading from the TPS. This causes more fuel than is required to be delivered to the combustion chamber, thus wasting an excessive amount of fuel.

When your fuel consumption starts going up for seemingly no reason, then you might want to check your TPS for problems.

#5. Limp Mode Activated.

Your car’s computer is likely very intelligent, and it can usually detect issues with your vehicle quickly. If it notices a problem with the TPS, then it might place your car into limp mode. This mode slows the vehicle’s ignition timing and reduces engine performance.

This is done to help prevent damage to your engine. It allows you to drive the vehicle to make it home or to a repair shop, but all the performance features of your car are disabled.

Any time that your car goes into limp mode, you should have it checked immediately by a mechanic.

#6. Difficulty Shifting Gears.

Believe it or not, your automatic transmission uses data about the position of your throttle to determine when to shift gears. It also uses this data to determine how firmly it needs to shift. If the data that it receives is incorrect, then it might have trouble shifting gears.

You might notice that your car is shifting gears too early, or it does not want to shift into the next gear on time. You might think that you need a transmission repair, but the problem could be related to your throttle position sensor.

#7. Weak Engine Performance.

When you press the gas pedal to the floor, you expect your vehicle to move quickly. If it doesn’t, it could be because the throttle valve is not opening wide enough. A bad TPS might be the cause of the problem.

You might find that you are pressing the gas pedal harder to get the same level of performance from your engine. If you find yourself in this situation, then consider testing your TPS. It could be faulty, thus causing problems with your throttle opening as it should.

#8. Jerking Or Bucking Of Vehicle.

This symptom is extremely obvious. Once the TPS completely fails, it will often cause your car to buck or surge as you drive. This is because the readings on the sensor fluctuate all over the place, and this causes your engine RPMs to rev high then drop low.

This constant fluctuation in RPMs causes a bucking of your vehicle as you drive. It might even feel like your transmission is slipping. This is extremely annoying to experience, and it can also be dangerous.

You should stop driving the car right away and have a mechanic check things out.

How to Test the Throttle Position Sensor?

If you own a multimeter, testing a TPS on your vehicle is a rather straightforward process. The following is a step-by-step guide on how to test a TPS sensor.

#1. Find the throttle mechanism.

The housing that is connected to the engine compartment will remain what it is. It will be the point from where the gasoline line branches off.

There will be a device attached to the throttle body which has cables leading to the engine control unit (ECU). This is the sensor for the position of the throttle.

#2. Find the wires that go to the power source, the ground, and the signal.

After you have determined the components, the next step is to locate the power, ground, and signal lines.

Simply said, this is due to the fact that all automobiles employ the same colors. The black cables represent the ground, while the red lines represent the electricity. The wire that carries the signal will be a different color, such as yellow, green, or blue.

#3. Examining the reference voltage.

Adjust the dial on the multimeter so that it reads volts. You will need to examine the voltage that serves as a reference. This demonstrates the voltage that is passing in between TPS and also the ECU.

To verify that it is working correctly, connect the negative meter probe to positive tab on the TPS wire and then connect the positive probe to the negative tab. If everything is functioning properly, the reading on the multimeter should be at about 5 volts.

#4. Evaluate the signal voltage.

At this point, you need to examine the voltage of the signal. In order to do this, you must first connect the positive probe to the signal wire tab, and then you must connect the ground probe to the frame of the vehicle. A voltage of half a volt is considered to be acceptable.

How Much Does a Throttle Position Sensor Replacement Cost?

Refer to this fair price estimate to ensure you’re paying the right amount for the sensor replacement.

A. Range

Overall, you may spend around $150 to $710 to replace the throttle position sensor (TPS), which includes:

• Parts cost: $100 to $540
• Labor cost: $50 to $170

NOTE: The TPS is removable in older vehicles with mechanical throttle systems, so the replacement is cheaper. However, the sensor is integrated with the throttle body in most newer cars with drive-by-wire systems. So, the entire throttle body has to be swapped, making it pricier.

B. Factors Affecting Cost

A few other aspects that can alter your final total include:

• Sensor type: Potentiometer-based sensors are commonly used in older vehicles, while newer cars use Hall effect-based sensors. Out of the two, Hall effect sensors are pricier because they’re more advanced.
• The complexity of the service: In older models, the sensor is fixed on the side of the throttle body (throttle valve spindle), so it’s easy to remove. But, in modern cars, it’s integrated with the throttle body housing and hence has to be replaced as one unit.  Replacing the entire throttle body needs more effort, resulting in higher labor costs.
• Recalibration costs: Sometimes, sensor recalibration is included in the replacement costs, but if it’s not, you’ll have to pay an extra $100 to $200 for it.

The Bottom Line

Your throttle position sensor is a critical component of your car’s fuel management system. Faulty TPS sensors can cause your vehicle to have odd symptoms that might even become dangerous.

You might find that the vehicle does not properly accelerate when you press the pedal, or it could start bucking and surging as you drive. Either way, you should get the issue corrected promptly. Thankfully, the repair is usually not very expensive.