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?
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).
Throttle Spring FAQ
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.
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.
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.
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.
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