Four common causes for a vehicle shaking while idle and their related parts.

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Is Your Car Shaking When Idle?

The shaking while idle is commonly caused by loose or broken engine mounts. However, it can also be caused by misfires in the engine due to carbon deposits and clogged fuel injectors.

Watch out: Experiencing your car shaking while idle can be pretty disturbing. It's a clear sign that something is wrong due to various issues. Not only can this shaking be annoying, but it can also lead to potentially dangerous traffic situations. In addition, your vehicle's performance and handling may be compromised.

The most common causes of the car shaking while idle

The most common causes for the car shaking while idle:

Faulty engine mounts: The motor mounts hold the engine, supporting it and keeping it properly aligned. However, due to wear, tear, aging, driving conditions, and recent accidents, a vehicle’s motor mounts might become loose, faulty, or leaky. These issues in a motor mount lead to excessive engine vibrations since there’s no proper support.
Shut idle air control valve: The idle air control valve (IAC) helps regulate the engine’s idle speed by controlling the amount of air passing when the throttle is closed. It basically ensures your engine remains stable when the car is sitting still. However, this valve can fail, resulting in engine unbalance and excess vibrations
Vacuum line leak: The vacuum line or vacuum hose is a tube that uses vacuum pressure from the engine to activate various other components like the brake booster, emissions control, etc. However, if the vacuum line is leaking, allowing air to escape, the vacuum pressure becomes unstable, resulting in excess vibrations in the engine.
Valve carbon deposit: If carbon builds up excessively on the engine's valves, it’ll cause misfires, resulting in worn spark plugs. This carbon buildup typically happens due to a lack of maintenance. Worn spark plugs cause spark issues in the combustion process, leading to excess vibrations in the engine.
Clogged fuel injector: The fuel injectors constantly spray fuel inside the combustion chamber while the vehicle drives, so it can provide the needed fuel based on engine demands. However, if the fuel injectors go faulty due to wear, damage, or carbon deposits, the fuel demand won’t succeed, resulting in engine misfires and combustion-related vibrations.

Frequently Asked Questions

Is the vehicle shaking if you stop it in gear and press brakes?

Your car has something called "motor mounts" that keep the engine in place. These mounts have rubber parts that prevent the engine from shaking too much when running normally. However, over time, the rubber can weaken and wear, allowing the metal parts of the mounts to touch each other. This contact causes the engine's vibration to transfer more to the car, making it shake. You might notice this more when stopping at a stoplight and pressing the brakes.
Have the vehicle's fuel economy suddenly worsened?

In a gasoline car engine, small parts called "fuel injectors" spray fuel into the engine before it ignites. Over time, these parts can get dirty and clogged from lack of maintenance. If that happens, the injector won't be able to spray the fuel, only dribble it out, making it harder to ignite. This causes the fuel to not burn completely in the engine cylinder, leading to lower performance and fuel economy.
Do you need to push the gas pedal to start your vehicle?

The idle air control valve is like a small motor that controls how much air goes into the engine when you're not pressing the gas pedal. This is important because you need enough air to help the engine run when you start your car. But if the valve gets stuck or breaks, it can close and shut out the air. This makes it hard for the engine to start, and you may have to floor the gas pedal to get it going.
Is the vehicle idling faster than usual?

The engine needs to know how much air is going into it to work correctly. This helps it determine how much fuel it needs to run smoothly. But if uncalculated air sneaks inside, it can mess things up. For example, this can make the engine idle (run without you pressing the gas pedal) weirdly. So, if too much air comes in, the idle might be too high.
Is the "check engine" light on the dashboard?

Engines in modern cars can put fuel directly into the engine part where it needs to go. However, this causes oil and gunk to build up on engine parts, preventing an ideal airflow. This buildup is called "carbon buildup" and can make the engine misfire. This can turn on the "check engine" light in your car.
Do you see thin oily spots on your vehicle's parking spot?

In your car, there are things called "motor mounts" that keep the engine in place and stop it from vibrating too much. Modern motor mounts have fluid to make them work even better. However, they can wear out and get hot over time, causing fluid leaks. As a result, you might notice black spots on the ground where you park your car.

Typical fixes to address the cause(s)

These are typical processes and repair services that fix a check engine light issue

The most common cause: Faulty engine mounts

The most common reason for a car shaking while idle is due to faulty engine mounts. The mounts that support the engine, keeping it aligned and tightly in place can loosen up, get leaky, bent, or break. In any case, if the engine mount loses balance, the engine loses support. Consequently, the vibrations that come from the engine combustion process will cause extra shakiness since the engine loses mount support.

Symptoms it causes: Apart from the vehicle shaking while idle you might notice the check engine light on, engine misfires, engine overheating, lawnmower sounds, banging and grinding noises, etc.
High risk of priority: A loose motor mount can quickly snap away, resulting in major damage in the engine compartment that might lead to engine stalling and a complete breakdown.

How exactly do the engine mounts fail?

Engine mounts are typically sturdy and reliable, made to last for decades. However, depending on driving conditions and recent accidents or improper restorations, the mounts can become unreliable and prone to bending and loosening up. If the mounts become loose, the engine loses support, resulting in excess vibrations, even when having the car at a standstill (idle).

Go safe: Ask for a mechanic to inspect your vehicle’s engine system to investigate if the engine mounts are faulty due to surrounding components and if there’s further damage to check out. Many shops do transparent vehicle inspections and lay out your options after investigating your vehicle’s conditions.

What’s a vehicle inspection? It’s “detective work” on your vehicle, checking its systems to see if anything prevents the car from working as expected. In this case, mechanics examine different parts of your vehicle to track if anything is causing the engine mounts to get faulty. They’ll also check the condition of components during their inspection, noting which are causing the problem and which got affected by it, recommending to replace them in order of priority.

Transparency example in a loose motor mount service

An engine system inspection is the most transparent process to understand why your vehicle’s engine mount is faulty. This is because many components surrounding the engine, support mounts, and combustion components can have a say in the issue, indicating the real culprits that caused it all.

A customer brought their vehicle to the shop and reported the engine was running rough and might need a tune-up.

The technician took the car for a test drive and noticed a lot of vibration through the vehicle when putting it in gear and pressing the brakes. However, they found no other issues related to the customer's concern during the vehicle health inspection.

To further diagnose the problem, the technician had an assistant get into the vehicle and, while in gear, torque the engine while pressing the brakes. They checked if the engine was moving excessively, but it did not appear to be.

Then, they lifted the vehicle on a hoist and manually pushed the engine at different locations to see if the vibration would disappear. It was found that raising the front of the engine eliminated the vibration.

Upon closer inspection, the technician noticed that the front engine mount had sagged and there was metal-to-metal contact. This means that the rubber on the motor mount deteriorated, and the metal engine mount was directly in touch with the car's metal frame, causing the vehicle to shake. Therefore, the front engine mount must be replaced to solve the problem.

Sagging motor mounts

In this case, the mechanic put the “Immediate Action” tag on the engine mount.

Similar Symptoms

Below are just a few examples of typical Symptoms and Fixes your car might be experiencing

Four common causes for a vehicle shaking while driving and their related parts.

Is Your Car Shaking When Idle?

The most common causes of the car shaking while idle

Frequently Asked Questions

Is the vehicle shaking if you stop it in gear and press brakes?

Have the vehicle's fuel economy suddenly worsened?

Do you need to push the gas pedal to start your vehicle?

Is the vehicle idling faster than usual?

Is the "check engine" light on the dashboard?

Do you see thin oily spots on your vehicle's parking spot?

Typical fixes to address the cause(s)

The most common cause: Faulty engine mounts

How exactly do the engine mounts fail?

Transparency example in a loose motor mount service

Similar Symptoms

Why Is My Car Shaking While I drive?

Why Does My Car Shake When I Brake At High Speeds?

Why Is My Car Shaking When Stopped?

Why Is My Car Shaking At High Speeds?

Why Is My Car Shaking When Accelerating?