5 Symptoms Of A Bad Throttle Position Sensor (and Replacement ...

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Though your car was running just fine the last time you drove it, it’s suddenly acting really strange. The idle may be surging, the car jerking while driving, and it might even stall out at a stop light. Your check engine light is probably on as well.

Without plugging in a code reader, it’s a good guess you’re having some sort of problem with the throttle position sensor. Here we go over how a throttle position sensor (TPS) works, go over the most common symptoms of a bad throttle position sensor, and provide some estimates on its replacement cost.

Table of Contents

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• Common Symptoms of a Bad Throttle Position Sensor
  • #1 – Check Engine Warning Light
  • #2 – Weak Acceleration
  • #3 – Engine Rough Idling
  • #4 – Excess Fuel Consumption
  • #5 – Unexpected Acceleration Changes
  • #6 – Transmission Issues
  • #7 – Car Won’t Start
  • #8 – Lack of Power When Towing
• Throttle Position Sensor Replacement Cost
• Common Misdiagnoses (When It’s Not the TPS to Blame)
• How a Throttle Position Sensor Works
• Electronic vs Mechanical Throttle Position Sensors

Common Symptoms of a Bad Throttle Position Sensor

If you have a bad throttle position sensor, then the engine control unit (ECU) will not know the position of the throttle. As a result, the engine control unit will not be able to properly regulate the amount of air that enters the engine so that a successful combustion can be made. This will ultimately impact your driving ability to the point where it is unsafe to stay on the road.

When your TPS is damaged or worn out, you’ll likely notice changes in your car’s behavior right away. While you may not recognize the TPS as the root cause, these symptoms should motivate to investigate further or get a professional diagnosis.

Related: Symptoms of a Bad Throttle Body

#1 – Check Engine Warning Light

The throttle position sensor is a key component of the overall internal combustion process. If this sensor goes bad, your engine will ultimately fail to produce sufficient power to accommodate your acceleration needs.

The engine control unit will detect this problem when it exists and then activate the Check Engine warning light on the dashboard. That way, you will be aware that your engine has some kind of problem that needs to be addressed.

A check engine light is one of the first signs of a faulty throttle position sensor. This is because the TPS monitors the throttle’s position and relays this information to the engine control unit. When the TPS malfunctions, it sends incorrect data (or no data), which in turn causes engine performance issues.

The car’s computer detects this inconsistency and triggers the check engine light to alert the driver of a potential problem requiring attention.

Common diagnostic trouble codes related to the TPS include: P0121, P0122, P0123, P0124, P2101, P2135, and P2138.

#2 – Weak Acceleration

With a faulty throttle position sensor, it may incorrectly signal that less power is required, even when the accelerator pedal is firmly pressed down.

This miscommunication results in reduced fuel injection and ignition timing, leading to sluggish acceleration and overall poor engine performance. Naturally, fuel consumption is also affected (as explained below).

#3 – Engine Rough Idling

When you stop or park your vehicle somewhere, its idle RPM shown on the tachometer in your dash should be somewhere in the vicinity of 600 to 900 RPM. If you notice the engine RPM below or above that range while your vehicle is stopped or parked, then you have a rough idle or fluctuating RPM problem with your engine.

This happens because when the TPS malfunctions, it may transmit inaccurate information about the throttle’s position, particularly at idle. This in turn causes the ECU to miscalculate the required fuel amount, leading to an improper air-fuel ratio.

As a result, the engine may receive too much or too little fuel, causing it to run unevenly or stumble at idle.

#4 – Excess Fuel Consumption

Since the throttle position sensor has a major effect on proper air/fuel mixture for burning, inaccurate readings can cause too much fuel to injected into the combustion chamber. This will cause a rich air/fuel ratio which will result in decreased fuel efficiency.

In addition, other sensors depend on accurate readings from the TPS. When that doesn’t happen, those sensors will often compensate for too little or too much airflow. The end result is usually the need to go fill up on gas more frequently than usual.

#5 – Unexpected Acceleration Changes

A malfunctioning TPS can send erratic signals to the engine control unit, causing unexpected changes in acceleration. This may result in sudden surges of power or drops in speed, even when the driver isn’t changing throttle input. The engine might rev unexpectedly or the car could lose power intermittently.

These unintended acceleration changes are obviously quite concerning as they can make the vehicle difficult to control and even dangerous to drive.

#6 – Transmission Issues

A faulty throttle position sensor can also affect automatic transmission performance. The TPS helps determine when it’s time to shift gears based on throttle position and engine load. When it malfunctions, incorrect signals may be sent, causing the transmission to shift at the wrong times.

You might experience harsh or delayed shifts, unexpected downshifts, or the transmission staying in a lower gear longer than necessary. Not only does this affect driving comfort but can also cause increased wear on transmission components. In some cases, the vehicle may even go into a “limp mode” as a protective measure, severely limiting how your car performs.

#7 – Car Won’t Start

In rare cases, a bad throttle position sensor can prevent your car from starting altogether. The engine control module (ECM) relies on input from the TPS to determine the correct amount of fuel to inject during startup. Without this info, the ECM may not initiate the starting sequence or provide the correct fuel mixture, making it impossible for the engine to turn over.

You might hear the starter motor engage, but the engine won’t catch. This symptom is often accompanied by other symptoms above including an illuminated check engine light.

#8 – Lack of Power When Towing

If you use your vehicle for towing, a faulty throttle position sensor can be particularly problematic. Towing requires precise control of the engine’s power output, which depends heavily on accurate throttle position information.

With a faulty TPS, the engine may not respond correctly to throttle inputs, especially under the increased load of towing. You might notice a major lack of power when trying to accelerate or climb hills while towing. Not only is this frustrating, but it also becomes dangerous when needing to navigate steep inclines or merging onto a highway.

Throttle Position Sensor Replacement Cost

Best places to order parts? See: 19 Best Online Auto Parts Stores

An engine needs the right amount of air just like it needs the right amount of fuel. If the engine does not receive the proper air amount, then its internal combustion process is compromised. This means inadequate power generation and a whole list of other problems.

You won’t be able to postpone this situation for too much longer. You’ll have no choice but to get a diagnostic check done on your vehicle by a certified mechanic.

If it is revealed that your throttle position sensor is bad, then you will need to replace it right away. The average replacement cost for the throttle position sensor is anywhere from $110 to $200. The parts cost is anywhere from $75 to $105 while the labor cost is anywhere from $35 to $95.

In addition, you will have to account for any extra fees and taxes that get added on as well. Overall, you shouldn’t have to spend more than $250 to get this replacement job done. If you shop around for an inexpensive mechanic, you might find a lower hourly rate.

Here’s a new section on Common Misdiagnoses for your article:

Common Misdiagnoses (When It’s Not the TPS to Blame)

Throttle position sensor symptoms are often mistaken for other issues. Recognizing these common misdiagnoses can potentially save you time and money.

1. Mass Airflow Sensor (MAF) Failure – The MAF sensor also measures air intake, and its symptoms can be similar to TPS issues. Both can cause poor acceleration and rough idling. However, MAF problems typically don’t cause the sudden acceleration changes associated with TPS failure.
2. Vacuum Leaks – A vacuum leak can cause erratic idling and poor performance, similar to TPS issues. However, vacuum leaks often produce a distinct hissing sound that TPS problems don’t.
3. Fuel Injector Problems – Clogged or bad fuel injectors can cause symptoms like rough idling and poor acceleration, which might be mistaken for TPS issues. However, fuel injector problems typically don’t cause the check engine light to come on as quickly as TPS issues do.
4. Ignition System Issues – Problems with spark plugs, ignition coils, or wires can cause misfires that might feel similar to the jerking associated with TPS failure. However, ignition issues usually produce more consistent symptoms across all driving conditions.
5. Catalytic Converter Blockage – A clogged catalytic converter can cause lack of power and poor fuel economy, similar to TPS issues. However, catalytic converter problems typically worsen gradually over time, while TPS issues often appear more suddenly.

How a Throttle Position Sensor Works

Every vehicle with an internal combustion engine has something called a throttle body, also referred to as a butterfly valve. This valve is positioned in the middle of the intake manifold and the air filter.

The job of the throttle is to manage the air flow that goes into the engine. As the driver steps on the gas pedal to accelerate the vehicle, more air is needed in the internal combustion chamber of the engine.

While more air enters the engine, more fuel gets injected into it as well. The ignition of this mixture is how engine power is created.

The position of the throttle determines how much air enters the engine. There is a component in the fuel management system called a throttle position sensor which detects this position.

When you want to accelerate the vehicle, the sensor gives the throttle position information to the engine control unit. From there, the engine control unit will manage the throttle and allow it to take in whatever amount of air is needed in the engine.

The harder you step on the gas pedal, the wider the throttle will open to allow more air flow into the engine. At the same time, more fuel will be injected into the engine cylinders to create a balanced mixture for combustion.

See Also: 3 Causes of an Electronic Throttle Control Light On

Electronic vs Mechanical Throttle Position Sensors

Throttle position sensors come in two main types: mechanical and electronic. The electronic version is often referred to as a “drive-by-wire” system. Here’s how they compare:

Feature	Mechanical TPS	Electronic TPS
Connection	Physical cable	Electronic signals
Sensor Type	Potentiometer	Hall effect or optical sensor
Design	Simpler	More complex
Precision	Less precise	More precise
Response Time	Slower	Faster
Durability	More prone to wear	Generally more durable
Maintenance	May require adjustments	Less frequent maintenance
Diagnosis	Generally easier	Can be more complex
Integration	Limited	Easily integrates with other systems
Failure Mode	May allow some manual control	Often has electronic fail-safe modes

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Mark StevensOwner at Car TreatmentsMark is a veteran auto technician who has honed his skills with over 19 years of service working at various independent shops. While Fords and Mazdas are his specialty, he enjoys working on practically any vehicle (except a Nissan 300ZX).He’s known for his attention to detail and problem-solving skills and enjoys coming up with out-of-the box solutions when the situation requires it.When he's not troubleshooting customers' cars, you'll most likely find him working on his current project ('96 Bronco) or cooking Italian food for his family. Latest posts by Mark Stevens (see all)

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