5 Symptoms of a Bad Throttle Position Sensor (and Replacement Cost)

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 bad throttle position sensor symptoms, and provide some estimates on its replacement cost.

How a Throttle Position Sensor Works

throttle position sensor

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.

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 you have a damaged or worn out throttle position sensor, you will notice the symptoms of this problem right away. You might not know it is the sensor’s fault, but the symptoms should motivate you enough to take your vehicle to the mechanic and find out what they think.

Chances are, they will tell you it is the throttle position sensor if you experience two or more of the following symptoms.

#1 – Check Engine Warning Light

check engine 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.

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

#2 – Weak Acceleration

reasons and causes of car not accelerating

A bad throttle position sensor means the engine control unit cannot manage the throttle position properly. The engine won’t be able to receive the proper amount of air because of this. Whenever you go to accelerate your vehicle under these conditions, the acceleration will be very weak.

You’ll be lucky if you can move the vehicle faster than 30 miles per hour. This will cause you to consume a lot of gasoline, and ultimately ruining your car’s fuel economy.

#3 – Engine Rough Idling

rough idling

When you stop or park your vehicle somewhere, its idle RPM 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 or erratic idling problem with your engine.

This may be due to a bad throttle position sensor if you’ve experienced some of the other symptoms on this list.

#4 – Excess Fuel Consumption

bad fuel economy

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 poor fuel economy.

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 – Acceleration Changes

car jerks when accelerating

One very strange acceleration problem that can occur is increased acceleration without stepping on the gas pedal. You could be driving along on the road, and your car will just speed up on its own out of the blue. This can obviously be very dangerous.

Out of all the acceleration problems that can occur, this particular one is a clear indicator that the throttle position sensor is to blame.

Replacement Cost

TPS replacement cost

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.



  1. In the heat of the day all of sudden I can’t get acceleration the check engine light do not come on .in the early morning no problems 2006 Chev Cobalt LS 2.2

  2. I have a 1992 Chevy Lumina APV Van with a 3.8 liter motor. I tested the old TPS and it shows as bad. It registers a constant 4.5 volts when I move the spring loaded tab on the TPS. The new one registers between .5 volts to a steady increase of 4.5 volts as it should when I move the tab. My idle is still super high. My question is does the little spring loaded bar on the TPS need to hook into something like the accelerator cable bracket maybe? Or, does the tab just need to rest against the bottom of the accelerator bracket/spring?

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