Car Shakes At Idle But Smooths Out While Driving

 Hello people, This article is going to take an in-depth dive into the possible causes for car shakes when idle but smoothing out while driving and further discuss the possible solutions regarding the same.

Car Shakes at Idle But Smooths Out While Driving 

It is crucial to understand the vehicle one drives. There is a huge risk to life if a vehicle is upholding some damage and is not attended to. A car shaking clearly indicates the need for mechanical attention and should never be neglected as a minor ‘not-a-big-deal’ issue as precautions are always better than a cure.

Without further ado, let us dive into the various reasons why a car shaking at idle but smooths out while driving:

1. Faulty Motor Mounts 

These are one of the leading factors that cause a car to shake at idle. But what exactly are motor mounts? Let us take a brief look at your engine’s anatomy. Motor or engine mounts are the components of your car that ensure that the transmission and engine are at the subframe. They also absorb shocks and vibrations while driving, ensuring that the driver does not suffer from any significant physical impact while driving. Simply put, it keeps the engine in place in its compartment to secure it while driving so it does not shake or move driving. 

2. Defective Spark Plugs 

The spark plugs are a crucial engine component as they provide the spark necessary to ignite the fuel in the combustion process. However, these spark plugs can become dirty and worn out over time, requiring periodic cleaning and inspection to ensure they function correctly. Failure to do so can cause the engine to experience increased stress during combustion, resulting in shaking at idle and misfiring.

3. Congested Fuel Injectors 

Shaky engines can often be attributed to clogged fuel injectors, which can occur when dirt accumulates in the fuel intake system over time. If these clogs are not addressed in a timely manner, they can damage the vehicle. The blockages can impede the supply of fuel to the engine, resulting in an inefficient combustion cycle and causing the engine to struggle. This is a primary factor responsible for the shaking of car engines.

4. Worn Out Belts and Hoses 

We all know that a car engine comprises various belts and hoses that work together for the engine to work. They need to be in perfect order to ensure a safe and smooth driving experience. A faulty hose or belt can create excessive noise and heavy vibration and even damage other essential parts of the engine if it breaks completely. 

5. Throttle Body or Defective Idle Speed Control

Passenger vehicles are typically designed to idle within a range of 600 to 1000 RPMs to prevent stalling and ensure the smooth operation of accessories like air conditioning.

However, it’s worth noting that certain car engines utilize idle control valves, which regulate the engine’s idle rotation speed. These valves can become contaminated with carbon deposits over time, causing them to function unpredictably. Engines that rely on electronic control mechanisms rather than idle control valves installed on the throttle body do not experience this issue.

After progressive use, the fuel intake system of a car suffers a toll. It can get contaminated, and its valves can even get clogged due to the same. If so, the engine fails to receive a steady, much-needed fuel supply, leading to vibrations while idling. The use of OBD2 scanners to keep a check on the engine. This is a cheaper and faster way to determine if the engine is facing issues on idle. 

7. Loose Battery Cables  

Having well connected battery cables in a car engine is crucial to a stress-free engine. If the battery cables run loose, there would not be enough power provided to the engine shaking at idle or not, not letting it start.

If you are working with an electrical system, the current needs to flow smoothly through its components which can only be done if all of them are connected tightly. If not, this seemingly small issue can even lead to misfires, leading the car to shake at idle because of the lack of compression due to the incorrectly firing cylinders.

This issue seems to go away when the car is driving as when the gas pedal is pressed and sped, extra power is used, which overcomes the said problem.

8. Oxygen Sensor 

Before we see how an oxygen sensor can cause car shaking at idle, let’s first understand what it and its significance is. An oxygen sensor is responsible for the exhaust levels in a vehicle to ensure the proper level of oxygen in it, not too little or too much, which are both harmful. A properly functioning oxygen sensor is essential to a car engine as it helps it determine the correct air and fuel ratio. If this does not work out properly, a rough idle problem can arise in the vehicle. It can even face difficulties to start. This issue happens if you’re idling or there is a drop in the fuel mileage.

How To Fix This Problem? | Car Shakes When Idle But Smooths Out While Driving 

Now that we have understood why a car may be shaking at idle but smoothing out while driving, let us look into a few possible ways to fix said problem. You may notice some of the given solutions to correspond to the stated above directly:

Replace Motor Mounts

As previously mentioned, motor mounts are a common culprit for causing a car to shake while idling. If your car is idling smoothly, there is a high likelihood that one or more of your motor mounts are defective. You can check this by attempting to move the engine freely in any direction to see if it feels loose. If it does, it confirms the presence of faulty motor mounts.

Replacing the motor mounts is the best course of action, as there aren’t many alternative methods. Replacing a motor mount typically ranges from $200 to $700, despite the actual mount costing between $50 to $150. The primary expense is the labor cost, so finding a reasonably priced mechanic before proceeding with the replacement process is essential.

Clean or Change Your Spark Plugs

A common cause of car shaking at idle is dirty or clogged spark plugs, which require regular cleaning to ensure the engine runs smoothly. One approach is to use a spray-on cleaner designed explicitly for spark plugs and a wire brush to remove dirt and debris from the plugs and electrodes.

However, it’s essential to avoid direct contact with the skin. Alternatively, you could replace the faulty spark plug. For an average vehicle, spark plugs range in cost from around five to twenty-five dollars, with some being challenging to reach.

Replace Worn-out Hoses and Belts

A fault hose or belt is best removed and replaced immediately. The cost for said replacement depends on the part of the broken component. For instance, a serpentine belt can cost upto three hundred dollars, whereas the belt alone can go upto the price of seventy-five dollars alone! While on the other hand, a vacuum hose ranges from a hundred to a thousand dollars, depending on the reach of the component and the place of a leak in the vacuum hose.

Get Your Idle Speed Control Checked

You can get your IAC and the throttle body of your vehicle cleaned. If that does not work or is not an option, replacement is your other way which can cost a hundred to five hundred dollars.

Inspection of the Fuel Intake System 

It’s essential to have your fuel intake system checked as part of your engine’s maintenance. During the inspection, you should also request that the mechanic examines the fuel pump.

The specific services required for your engine depend on its present condition. In some cases, a thorough cleaning may suffice; in others, a full service of the throttle plate, intake valves, and manifold may be necessary. The cost of these services can range from around $150 or more.


Some frequently asked questions about Car shakes when idle but smooths out while driving has been answered below:

Can a dirty throttle body cause shaking at idle?

Yes, it can. This can be caused by the lack of air in the engine. This can be fixed easily through a quick cleaning at your local mechanic or getting the component replaced altogether. 

Can low oil get my car to shake?

The car experiences more fiction when it functions with low oil, which can cause it to shake. You can avoid this by topping off your oil levels between oil changes but keep a mental note of how many times you do so.

How do I understand that my motor mounts are broken or faulty?

A faulty motor mount can be recognized by excessive vibration and an excessive lurch that does not sound healthy. Getting a mechanic to look into it is the best course of action.

Why does my car shake when I stop at a red light?

If your car is shaking when idle, then your worn-off or dirty spark plugs might be responsible for that. A faulty spark plug will make your car shaking when idle because it cannot ignite the piston cylinder fuel properly.

How often should you change spark plugs?

Spark plugs are engineered for long-term use and need to be replaced only after 80,000 to 100,000 miles of driving. Although, early replacements can also help you avoid costly engine repairs.


That is all I wanted to say on car shakes at idle but smooths out while driving. You should know what is best for your vehicle while driving it. Irrespective of whether your car feels faulty, you should take your vehicle to a mechanic to inspect it to ensure that all is well. Any sign of distress on your engine is the cause of concern and should be inspected by a professional immediately.

Remember, your safety lies in your own hands!

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