10 Symptoms of a Bad Throttle Position Sensor!

A bad throttle position is often an overlooked sensor that can make a car undrivable. Although there are ten symptoms to be aware of, they are all so closely linked you will probably experience more than one. Just for added measure, the symptoms of a failed TPS are similar to most other sensors that alter an engine’s air-fuel mixture, so diagnosing can be a little tricky. However, this article has you covered and how to reset the pesky sense.

The Role a Tps

The throttle position sensor, or TPS for short, is responsible for monitoring and providing information to the ECU about the position and movement of the throttle valve. Depending on how hard you press the gas pedal, that input opens the throttle body valve allowing more or less air into the engine. Knowing how open or closed the throttle valve is, the ECU can adjust the fuel delivery and ignition timing to suit.

10 Symptoms of a Failed Throttle Position Sensor

Let’s be realistic ten symptoms to look out for is a lot. If you notice one or 2 of the below, it might be that a bad throttle position sensor is the cause. But it will need further investigation.

  1. Poor acceleration and engine performance – The main problem with a failed TPS is the incorrect throttle valve position reading sent to the ECU. The valve could be fully open, your foot flat to the floor, and the ECU could think differently because of the incorrect information. The engine doesn’t receive the required fuel for the RPMs, and the performance suffers. You may also experience the engine jerking when holding a constant speed or delays when trying to accelerate.
  2. Sudden surges in RPMs – When the TPS sends incorrect information about the throttle valve position, the ECM adjusts fuel quantities. This can result in sudden increases in engine speed or RPM surges, but the car won’t move forward quicker. Essentially the ECU is trying to compensate for the irregular throttle position readings from the faulty TPS. These sudden surges in RPM can be unexpected.
  3. Rough idle and high RPMs – High idle RPMs and seeing the revs hunting is a sign that there is usually something wrong with the throttle body or the TPS is providing false information to the ECM. Incorrect information supplied to the ECM means the car will inject more or less fuel than needed or repeatedly alter the timing, meaning you will have a rough idle, and the RPMs may be sporadic.
  4. Engine misfire – Engine misfires are rare when the TPS is problematic and don’t happen often. The sensor must provide such bad information to the ECM for the timing and the air-fuel mixture to be so far apart it causes a misfire.
  5. Difficulty starting the car – The engine may struggle to deliver the required amount of fuel, making it challenging for the engine to start if the TPS isn’t operating correctly. You may experience extended cranking periods, but it will usually eventually start.
  6. Engine stalling – The engine stalling because of a faulty TPS will usually happen immediately after starting the engine or while idling. The car will struggle to adjust the air-fuel ratio while the engine reaches operating temperatures.
  7. Increased fuel consumption – Usually, when a TPS has failed, an increase in fuel consumption is noticeable. The engine will usually run much richer; you may also sense a strong gas smell when the engine is off.
  8. Check Engine Light on – The TPS is an electronic sensor, so if the ECU detects it isn’t providing accurate information, it will throw the light on the dashboard. The ECU can’t always determine the sensor is problematic, so the light may not always come on.
  9. Difficulty shifting gearsAutomatic transmissions use input signals, such as vehicle speed and engine load, to decide gear shifts. Based on the engine RPM and the throttle input, the ECU will delay upshift to allow you to accelerate or downshift if the revs drop. However, with a bad TPS, the shifting may not happen smoothly or at incorrect times due to the wrong throttle valve position signal provided.
  10. Problems with cruise control – This will not necessarily cause everyone an issue, but the cruise control uses the throttle valve and TPS to keep the car at the set speed. If the TPS sends a false signal to the ECU, the cruise control will keep dropping out. Basically, the car thinks you now have your foot on the gas pedal and back in control.

You may notice the three most common symptoms: sudden RPM surges, difficulty starting, and the check engine light on. When the check engine light illuminates, you can confirm a faulty TPS by plugging the car into an OBD2 diagnostic tool.

throttle valve plate

Can a Throttle Position Sensor Cause a Misfire?

Yes, a TPS can cause a misfire, but it’s not common. This is because its job is to provide the ECM with the throttle valve position so that it can make adjustments to fuel delivery and timing. Even with a bad throttle position sensor and drastic fuel delivery adjustments, the engine will run lean or rich—no misfire.

However, the TPS indirectly causes a misfire when it tells the ECM to alter the engine’s timing. It can cause the engine to fire early while it’s still injecting air and fuel into the combustion chamber, resulting in incomplete combustion, pre-ignition, and a misfire.

Can You Drive With a Bad Tps

Although driving with a bad TPS is possible, it’s not recommended. A bad TPS can result in poor acceleration, hesitation, and difficulty maintaining a consistent speed. These problems can make driving unpredictable and potentially dangerous, especially when you need immediate throttle response to get you out of trouble.

How to Reset a Throttle Position Sensor

Sometimes you can reset a faulty throttle position sensor rather than just replacing it. I would use the following steps to reset a TPS:

  1. Turn off the engine, remove the key from the car, and disconnect the negative terminal (black cable) from the battery.
  2. Locate the TPS, which is usually mounted on the throttle body or attached to the throttle plate.
  3. Unplug the electrical connector from the back of the TPS. You may need to press a release tab or squeeze the connector to disconnect it.
  4. Leave the TPS disconnected for about 1-2 minutes to allow any residual charge to dissipate. Then, reconnect the electrical connector to the TPS.
  5. Reconnect the battery and start the engine. Allow it to idle for a few minutes, but do not rev or drive the car. The ECU will ‘recalibrate’ and understand the idle throttle valve position depending on how bad the TPS was.
  6. After resetting, test the TPS functionality by gradually pressing and releasing the throttle pedal to ensure a smooth and responsive throttle response.

If the engine management light comes on the dashboard at any point, you may need to clear the fault code. Once cleared, if the fault light comes back on, the TPS cannot be saved and will need replacing.

Final Words

By identifying symptoms of a bad throttle position sensor, you can resolve the issue, ensuring the car drives smoothly and operates correctly. Or you can at least determine it’s not the faulty TPS and something completely different causing a problem.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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