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Summary
  • A throttle spring can refer to a small spring around the throttle shaft that returns the throttle shaft to its original position after you release the acceleration pedal.
  • In other applications, a throttle spring is a linear spring with hooks on both ends. One end is connected to a bracket, while the opposite end is hooked to a throttle lever.
  • Some of the symptoms of a bad throttle spring include a stuck gas pedal, a high idle speed, and a clogged throttle body.

Unless you own a drive-by-wire vehicle, your vehicle most likely has a throttle return spring. This spring is responsible for closing your vehicle’s throttle valve after you open it by accelerating. If the spring is disconnected or broken, the throttle may not return to idle after you release the accelerator. Electronic throttle bodies have a return spring as well, but that’s not what closes the throttle on an ETC system; the motor drives the throttle closed.

What Is a Throttle Spring?

throttle return spring diagram
Diagram of a throttle return spring | Image Source: Richard McCuistian

A throttle return spring can either be a small spring around the throttle shaft that returns the throttle shaft to its original position after you release the accelerator pedal or it will be a linear spring with hooks on both ends connected on one end to a bracket with the opposite end hooked to the throttle lever.

If the throttle spring is disconnected or broken, the throttle may not return to idle after you release the accelerator.

Richard McCuistian, ASE Certified Master Automobile Technician

Symptoms of a Bad Throttle Spring

Stuck Gas Pedal

A stuck accelerator or gas pedal can be a sign of a bad throttle spring. Because the spring is broken, it can no longer provide enough tension to close the butterfly valve. When you take your foot off of the accelerator, it might return to its position very slowly or not move at all. This can be dangerous, especially when driving in heavy traffic.

Keep in mind that a sticky gas pedal can also be a sign of other throttle issues, so it’s best to bring your vehicle to a mechanic for a thorough inspection.

High Idle Speed

If you start noticing your vehicle has an unusually high idle speed, it might be because of a bad throttle spring. A faulty spring won’t be able to close the throttle valve, and a throttle valve that won’t close introduces more air in the engine, causing an increase in idle speed. A high idle speed can waste fuel and damage your engine, so it’s best to replace your faulty throttle spring as soon as possible.

Clogged Throttle Body

Your vehicle’s throttle body will accumulate dirt, grime, and soot over time, but a bad spring can cause it to clog faster. A spring with no resistance can no longer close the valve, which will allow air to freely enter the throttle body. This increases the chances of more dirt entering the engine, which will eventually clog the throttle and prevent air-fuel flow.

What Does a Throttle Spring Do?

While the throttle cable pulls the valve open, the throttle spring closes it. When you press on the accelerator pedal, the throttle valve opens to allow more air to enter the engine. Then, the engine releases more fuel to balance the air-fuel ratio, resulting in an increase of power and speed. Taking your foot off the pedal will allow the throttle return spring to push the valve closed.

The spring also holds the valve in a default position, also known as the neutral or fail-safe position. This varies per vehicle, but in general, a neutral position means the valve is 16% to 20% open. This results in a speed of 1200 to 1500 revolutions per minute (RPM).

tachometer showing an idle speed
A faulty throttle spring won’t be able to close the throttle valve, and a throttle valve that won’t close introduces more air in the engine, causing an increase in idle speed.

Throttle Spring FAQ

Can You Drive With a Broken Throttle Return Spring?

While a broken spring won’t stop your engine from running, it isn’t a good idea to drive around with one. A broken spring can make it hard for you to accelerate, which puts you and your passengers at risk of traffic accidents. It’s best to take your vehicle to a mechanic as soon as possible if you suspect it might have a faulty throttle spring.

Do All Vehicles Have a Throttle Spring?

Not all vehicles have a throttle spring. Vehicles with an electric throttle control (ETC) or a drive-by-wire system use an electric actuator motor instead of a mechanical cable. The ETC system opens the throttle valve electrically, so it no longer needs a spring to open and close the plate.

How Often Should You Replace Throttle Return Springs?

Unlike most parts of your vehicle, throttle springs don’t require regular maintenance or servicing. A high-quality spring usually has a similar lifespan to your vehicle. However, if it isn’t installed correctly, it can wear out and break over time.

How Much Does a Throttle Spring Replacement Cost?

The price can vary based on several factors, such as your vehicle’s make, model, and the product’s brand. In general, most throttle springs cost less than $10, while some replacement kits can cost you around $25.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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