It Shakes at Idle but Smooths Out While Driving

When you hit the road, you expect a smooth ride, but that’s not the case when something malfunctions. Strange things can happen when your car shakes while it is in motion but becomes smoother as you drive. People can be left wondering if this is normal. A lot of people might wonder if it is even safe to drive. 

Each of these problems are examined to find the best solution. The average price of every repair is also listed in our guide. 

Why Car Shakes At Idle, But Smoothes Out While Driving

Motor mounts may be the cause of jerks in idle and smoothening out during driving. You may also notice a faulty idle speed control, fouled spark plugs or worn belts. Finally, you need to examine the fuel intake system to see if that’s to blame. 

1. Bad Motor Mounts

Motor mounts secure your engine to your car. The motor will not stay still if the mounts fail or wear. 

The vibration is most noticeable when the vehicle is idling, or even stopped. If the shaking ends once you put your vehicle in Neutral, it’s a tell-tale sign that the mounts need to be replaced. The shaking might not be as noticeable when the vehicle moves. 

2. Fouled Spark Plugs

Sometimes, you may only need to change the spark plugs. If these components become clogged or corroded, the spark plugs can cause firing to be incorrect. Because the fuel can’t ignite properly in the cylinders, the engine could start to misfire or shake.

It is possible to have prevented this issue. It’s best to change the spark plugs as part of your regular maintenance tasks, with appropriate intervals ranging from 30,000 to 150,000 miles, depending on the type of plugs you use. 

Related: Car Shakes When Idling Or Stopped? (Here’s How to Fix it)

3. Worn Belts/Hoses

Many belts and pipes are necessary for smooth riding. A defective belt or liner can cause vibration and excessive noise.

Think about how important the serpentine belt. A worn or damaged belt could cause additional vibration and shaking. 

Vacuum hoses might be responsible for shaking the engine violently. This can cause engine surging and hesitation which will result in reduced performance.

4. Throttle body or defective idle speed control

Most passenger cars are engineered to idle at 600-1000 RPMs. While running at this rate, the engine shouldn’t stall. The engine is also able to power the air conditioning unit and any other accessories. 

Some engines have an idle control valve, or IAC. The idle speed is controlled by this device. This device can be contaminated by carbon deposits that could cause it to malfunction. 

However, not all cars have IAC. In fact, many modern cars use electronic control measures on the throttle body, so this option won’t be an issue for most people. 

5. Malfunctioning fuel intake system

The fuel intake could be the cause of your car shaking, vibrating or shaking during idle. The fuel intake system can take a beating as you drive your car. The fuel intake system becomes dirty and contaminated. Extreme cases can lead to clogging of valves from the accumulation. 

If the valves are obstructed, the engine can’t receive a steady, constant supply of fuel. Uneven fuel supply can lead to engine vibrations when the engine is idle. 

To check trouble codes, use an OBD2 scaner if the engine seems to be having problems at idle. You will be able to identify the problem faster and more cost-effectively. You should check your spark plugs or ignition coils if you have misfiring codes.

How to fix a shaking car at Idle

1. Repair or Replace the Motor Mounts

The motor mounts could be faulty if the engine moves a lot while it is running. To test if the engine feels loose, push it in various directions.

Motor mounts that are damaged must be repaired to prevent shaking. It costs between $200-$700 to replace motor mountings. It all depends on how difficult it is to reach the mounts. 

The cost of motor mounts is between $50 and $150. Most of the cost will go for labor which could add up to $150-$550 to your total bill. 

2. Use clean/change spark plugs

The spark plugs could be bad if your car has a problem with idle. You can clean the spark plugs if they are dirty. You can clean your electrode with a special spray-on cleaner for spark plugs. 

It might not be as expensive to change contaminated spark plugs, but it may still make sense. You can buy spark plugs in most cars for as low as $5 or $25. Most expensive is labor to replace plugs. This is especially true if the job is difficult. 

3. Replace Worn Belts/Hoses

There are many factors that affect the cost of replacing a worn belt, hose or other component. A serpentine belt can be replaced for $100-$300. While the belt may cost between $25 and $75, labor can run $75 to $225. 

A vacuum hose replacement might run between $150 and $1,000. It depends on how far the vacuum leak is located and what difficulty it takes to reach. 

4. Adjust the idle speed control

It’s possible to clean the IAC, along with the throttle body. It’s often found on the intake manifold towards the rear of the throttle body.

If cleaning the IAC doesn’t work, replacing it is the only option. You could end up paying anywhere between $100-$500. The parts typically make up between $50 and $300 of the total cost. 

5. Service Fuel Intake Systems

You can inspect the fuel intake to identify any issues. It’s also wise to check the fuel pump during this examination.

The needs of your vehicle will determine the cost of fuel induction services. Sometimes a fuel induction cleaning is all that’s required. Other times the intake valves, throttle plates, and intake manifold need service. 

Full fuel induction services can cost up to $150. To circumvent this cost, some people choose to use fuel injection cleaner, but that doesn’t always solve the problems.