Car Shakes At Idle But Smooths Out While Driving

Ever heard someone complain that his car shakes at idle but smooths out while driving? Or are you currently experiencing this kind of challenge with your vehicle? It can be so disheartening, especially when you have no clue what could be wrong.

This problem is not necessarily a hard nut to crack when you understand the causes and how to fix them appropriately. Let’s find out what causes a car to shake when idle and smooths out while on the road.

What Causes A Car Shakes At Idle But Smooths Out While Driving?

There are several reasons why a car shakes when idle and accelerating. The problem can range from defective motor mounts to faulty spark plugs, and so on.

In any case, it is crucial to examine your car for any of these challenges if your car vibrates when stopped in gear.

Car Shakes At Idle But Smooths Out While Driving

Defective motor mounts

A vehicle’s motor mounts help to hold the engine in place within its compartment so that it doesn’t move or shake when running.

The motor mounts (sometimes called engine mounts) keep the transmission and engine to the subframe and at the same time absorb shocks and vibrations so that the driver does not feel any of such impacts when the vehicle is running.

When the motor mounts break, it can no longer hold the engine properly in place, thereby resulting in uncontrollable shaking and vibration.

Bad spark plugs

A vehicle’s spark plugs play a significant role in the combustion process; they provide the spark that helps the engine ignite the fuel.

If any of the sparks plugs become worn out or dirty, they will not be able to function properly, thereby causing the engine to exert more stress in the combustion process. When this happens, the engine will misfire and shake randomly.

Clogged fuel injectors

A car’s fuel injectors or fuel intake system can be blocked with dirt over time. If you fail to remove the clogs, they will hinder the fuel supply process to the engine and cause it to struggle to complete a combustion cycle. The uneven supply of fuel will cause the engine to shake.

Loose hoses

A vehicle’s vacuum hoses help to eradicate exhaust fumes, which are by-products of gasoline. If you have a broken or loose vacuum hose, the leakage will hinder the process of clearing the gasoline by-products, and this can lead to engine shaking.

Worn-out belts

A worn-out timing belt is another reason a car would shake when idle. Loose or worn-out belts can affect the proper functioning of the fans within the engine compartment, resulting in loud noise and shaking when a vehicle idles.

What Does It Mean When Your Car Shakes While Sitting Still?

When your car shakes while sitting still, it is most likely that the motor mounts are disconnected from the engine or broken. The motor mounts are responsible for keeping your car’s engine attached in place within the engine compartment.

Therefore, if the motor mounts are broken or disconnected, they can no longer hold the engine in place, resulting in a sporadic shaking. The shaking can be excessive to the extent of impacting the entire car.

In order to diagnose this kind of challenge, put your car’s gear on neutral (N) and observe the shaking for a moment. If the shaking reduces, it is obviously a challenge from broken motor mounts. It is crucial to fix the issue immediately to avoid further damages.

How To Fix Car Shakes At Idle But Smooths Out While Driving

Once you diagnose your car’s engine and other components to ascertain the specific cause of the shaking, it is essential to verify the faults that you can easily rectify, especially as a DIYer, and contact an expert auto mechanic in cases that require a professional’s service.

Fixing the problems outlined above will not cost a fortune. However, if you neglect them, they may result in further damages. The following recommendations will help you handle the issues stated above.

  • Contact a mechanic to fix the broken motor mounts.
  • Replace defective spark plugs.
  • Replace clogged fuel injectors.
  • Reconnect loose hoses and replace any broken vacuum hose.
  • Replace timing belt.

Most of the replacements outlined above will require the service of a professional auto mechanic. However, a few parts may be easy to replace for people who are used to performing minor repairs on their vehicles by themselves.

why is my engine shaking when idle


Q: Is it normal for a car to shake a little when idle?

It is quite abnormal for a car to shake when idle, no matter how little it shakes. If a car shakes when idle, it is a sign that something could be wrong with the engine mounts.

Also, a shaky idling vehicle may result from faulty engine components such as timing belts, spark plugs, or fuel injectors.

If your car shakes when stopped with AC on, it would be in your best interest to take a moment and find out what could be wrong in order to avoid further damages or risk. If you can’t figure out the problem by yourself, ensure to contact an expert auto mechanic to check it out.

Q: Why does my car vibrate so much when idling?

If your car vibrates so much when idling, you most likely have defective motor mounts. A car’s motor mounts are responsible for dampening the vibrations, especially when the car idles.

Broken motor mounts will automatically be unable to dampen a vehicle’s vibration; hence you will eventually feel so much vibration when your car is idle.

If your car vibrates when idle and AC is on, kindly take a moment to ascertain whether the car’s motor mounts are defective; in order to do that, switch the gear to neutral (N) and observe it for a moment. If it reduces the shaking, it means you most likely have broken motor mounts.

Q: Can clogged fuel injectors cause vibration?

Of course, clogged fuel injectors can cause vibration in a vehicle. So, it would be best if you do everything possible to avoid your car’s fuel injectors from getting clogged with dirt.

A clogged fuel injector will automatically hinder the corresponding cylinder from its ability to fire adequately.

When a cylinder fails to fire correctly, the engine will find it challenging to finish each combustion cycle due to insufficient fuel, resulting in engine vibration. If you experience this kind of situation, ensure to contact an expert auto mechanic immediately.

Q: Can a bad spark plug cause car to shake?

A bad or defective spark plug can be a culprit to a car shaking when idle. Faulty spark plugs result in uneven burning of fuel during the combustion process in an engine. When this happens, the RPMs will fluctuate, and the engine will produce a loud noise.

Besides the loud noise and fluctuating RPMs, the car’s engine will start to vibrate as a result of the force the engine exerts to finish a combustion cycle due to a bad spark plug. The vibration can extend from the engine to every part of the car.

Q: Can a bad battery cause my car to shake?

A defective battery cannot generate sufficient power to keep a vehicle’s engine running, thereby making the alternator work harder for the engine to keep running.

The stress that the engine exerts to stay running due to insufficient power from the battery will eventually cause the car to shake, stall, and sometimes stop.

A car’s battery is one of the essential components that enable a car to work efficiently; otherwise, the consequence of having a defective battery can be so frustrating, especially when it leaves you stranded.

Final Words

Most of the reasons why your car shakes at idle but smooths out while driving, as well as the solutions to the problems, have been addressed above in this article. If you have a friend who says, “My car shakes when I drive,” you may want to refer them to read this article.

It is crucial to fix mechanical faults early enough before they escalate into more complicated problems. So, if you are currently facing this challenge, ensure to follow the recommendations above or contact an expert auto mechanic to diagnose and fix the problem.

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Osuagwu Solomon

Osuagwu Solomon is a seasoned automotive technician for the past 9 years, and a technical writer. He loves writing about auto professional repair guides, DIY repair guides, and buyer’s guide. After spending six years in the automotive workshop, he decided to impact his knowledge to people aside his domain, and he has achieved this by centering his Automotive writing skills on REPAIRS.

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