Engine Shakes When Idling: 4 Potential Causes and How to Fix Them

What Causes an Engine To Shake When Idling? In-Depth Causes With Potential Solutions

All vehicles that use an internal combustion engine are known to vibrate and shake, especially when running. The vibrations are mostly due to the piston motions, rotating parts, and combustion forces.

However, the shaking should not be excessive such that they are noticeable to the car’s owners while idling. When the engine shakes a lot while idling, various causes are potentially behind it.

The following list contains potential causes for the engine shake while your car idles;

1. Broken Motor Mounts

One of the primary reasons your car engine shakes while the vehicle idles is due to broken motor mounts. Motor mounts, also called engine mounts, are components that hold the vehicle’s engine to the car’s frame.

Motor mounts help minimize the engine’s vibrations; if broken or loose, your car’s engine will shake a lot, even while idling. Speed driving in uneven terrain and damage to the motor mount rubber are among the reasons the mounts loosen and brake.

Diagnosis

Diagnosing broken motor mounts as reasons behind the car shaking while idling includes visually inspecting them. Pop the vehicle’s hood and attempt to shake the engine. Usually, it should feel stiff and should not move. Large cracks on the motor mount rubber mean it’s faulty.

Also, have someone press the gas pedal while you are looking at the engine. The motor mounts are broken or damaged if the car engine tilts in any direction when the gas pedal is depressed.

Solutions

Motor mounts are often irreparable; the safest and best solution is to replace them. Buy the motor mounts compatible with your vehicle (check the user manual) and follow the steps below to replace them;

• Step 1. Locate the motor mounts. There are usually two or four at the bottom of the car engine (depending on your car).
• Step 2. Remove any component above the mounts, like water reservoirs or air filters.
• Step 3. Access each motor mount, unscrew it and install a new one.
• Step 4. Test engine for play

Replacing motor mounts costs between $400 and $1,000. The cost varies with car type.

Below is a video showing how to replace the motor mount in a car.

2. Spark Plug Issues

The purpose of spark plugs in the engine is to create a spark during the compression stroke. When the spark plugs fail, the air and fuel mixture is unburnt, causing an engine misfire.

Misfire causes the engine to shake due to the uneven combustion happening in the car’s engine.

Diagnosis

A failing spark plug has many tell-tale signs that you can use to confirm it as the reason behind the engine shaking. Some of the signs to look at include;

• Trouble starting the car
• Rough idle
• High gas mileage

Also, access the spark plugs and visually inspect them for signs of burning. Read the steps under the solutions.

Solutions

A problematic spark plug needs replacing, and it’s a good habit to change all of them at once. Therefore, buy the manufacturer-recommended spark plugs (consult the user manual) and follow the steps below to replace them;

• Step 1. Locate the spark plugs. They are usually on the engine’s top side with wires connecting to them.
• Step 2. Disconnect the electrical wires connecting to the spark plugs.
• Step 3. Use a socket wrench to remove the spark plug.
• Step 4. Install the new spark plugs using a torque wrench so as not to over-torque them. Tighten each snugly to prevent sticking the next time you remove them.
• Step 5. Repeat the steps on other cylinders.

Spark plugs cost between $9 and $25, and the labor cost falls between $40 and $360.

The following video shows how to change and inspect spark plugs.

3. Fuel System Issues

An issue with the fuel system can also be behind the engine shaking when idling. The system delivers fuel to the engine for combustion, and if it develops an issue, the car engine gets little or no fuel.

The engine then misfires, and like in the earlier case of the faulty spark plug, the vehicle shakes. A clogged fuel injector or a problematic fuel pump are the two parts of the fuel system that can cause this issue.

Diagnosis

Check for the following signs to diagnose fuel system issues as the cause of the engine shaking.

• Engine sputtering
• Engine misfire
• Power loss
• Fluctuating RPM needle
• Low or lack of fuel pressure

Solutions

The solution to an issue with the fuel system is to repair or replace the faulty part. Buy a new fuel injector and (or) fuel pump. (Consult the user manual for the right types.)

Follow the steps below to change the fuel injector.

• Step 1. Disconnect the battery and let the vehicle cool
• Step 2. Locate the fuel injectors. They’re usually on the intake manifold
• Step 3. Remove the connectors and the fuel rail
• Step 4. Wiggle and remove the old injectors
• Step 5. Install new injectors
• Step 6. Install the fuel rail and plug in the connectors
• Step 7. Test the vehicle

The following video shows how to replace the fuel injectors.

Follow the steps below to replace the fuel pump.

• Step 1. Jack up the vehicle
• Step 2. Unscrew and remove gas lines
• Step 3. Unscrew and lower the gas tank
• Step 4. Remove the cover to the gas tank
• Step 5. Remove the plastic assembly inside the gas tank
• Step 6. Remove the old pump and install a new one
• Step 7. Replace the pump inside the assembly and push it into the gas tank
• Step 8. Reinstall the gas tank cover and put the tank back in position
• Step 9. Screw the gas tank and reinstall the gas lines
• Step 10. Test the car for vibration

The following video shows how to replace a fuel pump in a car

Both repairs will cost you between $450 and $1200.

4. Idle Air Control Valve Issues

An issue with the idle air control valve will cause the engine to shake when it idles. The valve regulates airflow to the car’s engine as it idles to prevent stalling. Lack of maintenance or use of incompatible or poor-quality fuel causes issues with the valve to develop.

Diagnosis

Check for other signs like what we have below.

• High idle speed
• Irregular idle speed
• Stalling
• Check engine light turns on

You can also use a scan tool to check for codes related to the Idle control system malfunction, like code P0505.

Solution

A faulty idle control valve needs replacing or cleaning. Purchase a new valve compatible with your vehicle and follow the steps below to repair or replace it;

• Step 1. Locate the idle air control valve. The valve is usually in the intake manifold.
• Step 2. Unscrew the two bolts holding the valve on the throttle body.
• Step 3. Remove the valve and clean the inside of the throttle body.
• Step 4. Clean the valve by spraying a carbon cleaner. Then, reinstall it.
• Step 5. If cleaning doesn’t work, then replace the old idle air valve with a new one.
• Step 6. Test the valve.

The following video shows how to replace an idle air control valve.

Most repair shops will cost you between $200 and $400 to replace an idle control valve.

Why is the engine rocking at idle? What could be the cause?

If you find your engine rocking at idle, experiencing turbulence akin to an airplane mid-storm, it’s essential to address the issue promptly. Your car, though supposed to remain stationary while idling, might exhibit unsettling vibrations. Before resorting to a Google search for “Why does my engine shake?” consider crucial factors.

Your car’s idle speed control, managed by the idle air control (IAC) valve, can accumulate carbon deposits over time, affecting its efficiency. Engine mounts, comprising rubber blocks, support the engine and may wear down, transmitting vibrations to the frame. Spark plugs, if dirty or worn, can cause misfires, while a faulty fuel intake system or loose hoses/belts may disrupt a steady fuel supply.

If you notice your engine shaking, it’s imperative to consult a mechanic promptly for a thorough diagnosis and resolution of issues, ensuring your car runs smoothly both at a standstill and on the road.

If your vehicle experiences engine shaking when idle, you might find our articles on ‘Engine Vibration When Decelerating: Know The Causes And Solutions’ and ‘Engine Shaking and Loss of Power: 5 Possible Causes and Solutions’ beneficial, encompassing all the necessary information. Our article on engine vibration when decelerating provides an in-depth look at the reasons behind the problem and lists a step-by-step solution guide for addressing each issue. Meanwhile, our article on engine shaking and loss of power explores everything you need to know!

Related Questions

This section lists some questions you might ask yourself about the engine shaking while idling.

Q1. Can I Drive a Vehicle Which Its Engine Shakes When Idling?

While you can drive a car with a shaking engine at idle, it’s usually not recommended. Get the car diagnosed and fixed to prevent more issues from developing.

Q2. How Long Does Fixing Engine Shaking When Idling Problem?

It will take between 30 minutes to four hours to diagnose and fix the engine shaking at idle problem. The time varies with the exact cause behind the issue.

Final Words

In summary, if your engine shakes when idling, the first thing to check should be the motor mounts. If they are fine, check for other issues, like an idle control valve, fuel system, and spark plug issues.

To pinpoint the exact issues, perform further diagnostic tests and check for signs and symptoms discussed in the article. Also, follow the steps mentioned under each issue to fix it. Hire a mechanic to handle the repairs and replacements if you’re uncomfortable handling them.