Car Shaking After Changing Spark Plugs – Why?

A car shaking after changing spark plugs is a typical example of vehicle malfunction. It can be somewhat confusing to figure out the problem. However, a careful diagnosis will reveal the cause of the problem. If you have defective spark plugs or wrong fitted plug wires, you can face car vibration even after replacing the old plugs.

Therefore, if you’re currently experiencing this kind of situation, carefully find out why your car shakes after replacing the old spark plugs and what to do about the issue from this article.

car shaking after changing spark plugs

Why Is My Car Shaking After Changing Spark Plugs?

There are two basic reasons why your car shakes after changing the spark plugs. Firstly, it could be due to the plug cables not fitting properly onto the spark plug terminals.

The poor connection can result from fixing the leads in a hurry without properly pushing them to snap or click on the terminals. So, when you start your vehicle’s engine, the plugs will not be able to function effectively under this condition.

Secondly, if your car vibrates after changing spark plugs, it can also indicate that you probably have one or more defective spark plugs. You can also face shaking due to wet black spark plugs. Can bad spark plugs cause car to shake? Of course! In this case, it could be that the new spark plugs were damaged at the factory or during installation.

So, if you’re facing this kind of challenge now, carefully inspect the connection between the spark plug leads and their respective terminals to ascertain a proper connection. Also, take a moment to check if any of the plugs are damaged.

If you identify any defective spark plugs, replace them immediately and start the car to verify if you have successfully resolved the problems.

How do you stop carbon buildup on spark plugs?

Car owners can take several steps to prevent carbon buildup on spark plugs. First, ensure that the spark plugs are the correct size and type for your vehicle, as specified in the vehicle’s manual. A common type of high-performance one is the PFR8S8EG, designed to resist carbon deposition. When installing new plugs, follow the manufacturer’s guidelines to avoid issues like car shaking due to improper installation.

Regular maintenance of auto parts is crucial. Use high-quality spark plug wires and ensure they are accurately connected to the spark plug terminals, avoiding power leakage that can lead to suboptimal spark efficiency and contribute to carbon build-up. The ignition voltage should be checked periodically; a weak spark can cause incomplete combustion, leading to carbon deposits.

Modern spark plugs often have a self-cleaning temperature, which achieved when the engine runs at highway speeds. This helps to burn off impurities that can cause carbon deposit damage. Additionally, maintaining the engine’s overall performance by using good quality fuel and ensuring the fuel-air mixture is correct can prevent the conditions that cause carbon deposits.

In cases where carbon buildup is a recurrent problem, providing feedback to a qualified mechanic can result in an analysis to identify and resolve underlying issues, such as insulator protrusion or metal housing defects.

Common Causes of Car Shaking

Defective tires or wheels, broken mounts, and engine misfiring are the major causes of car shakes when accelerating but not when coasting. However, the problem can be multi-dimensional.

For example, a wheel defect can be due to loose lug nuts, uneven tire wear, improper wheel balance, or separated tire treads. Let’s see them in detail.

Loose lug nuts

Loose lug nuts are common when you fail to properly tighten the bolts or nuts when changing your tires. This will eventually cause the tires to shake when you’re driving because they are not firmly held against the hub.

Uneven tire wear

Improper alignment, under inflation, over inflation, or a worn-out suspension can cause uneven tire wear over time, resulting in an imbalance between two opposite tires (left and right). This can cause your car to shake on the road until you get a replacement.

Improper wheel balance

Wheel balancing helps you keep your tires in a correctly angled position. If you fail to balance your vehicle’s wheels after changing the tires, you will eventually experience vibrations when driving. Proper wheel balancing will resolve the issue immediately.

Separated tire treads

Manufacturing errors, rough driving style, or tire over usage can cause a separation in a vehicle’s tire treads. The separation occurs when the tire’s tread comes apart from the body or casing of the tire. When this happens, you will feel a strong vibration when driving.

Broken transmission mount

A bad transmission mount will not only result in gear shifting difficulty, it can also lead to clunking or clanking noise and excess vibrations when a car is running.

Broken engine mount

The engine mount links a vehicle’s engine to the body. In addition, it helps to dampen vibrations from the engine. Therefore, a broken engine mount will automatically result in vibrations from the engine due to the misalignment between the engine and the vehicle’s body.

Engine misfiring

Lousy spark plugs, defective spark plug wires, faulty ignition coil, and lean air-fuel mixture are some of the causes of engine misfires. Meanwhile, when a misfire occurs, car shakes after changing ignition coil.

Bent driveshaft and axle

Usually, a vehicle’s driveshaft bends over a while. Meanwhile, a bent axle is often caused by an accidental collision. Therefore, if you notice a horrible shaking when driving, especially around 40 – 50 mph, verify if a bent axle or driveshaft is responsible for the vibration.

Does Fixing Spark Plugs Stop Vibration?

Of course, changing spark plugs can stop a vehicle’s engine vibrations if faulty spark plugs are the cause of the problem. In other words, if your car’s engine is shaking due to a cylinder misfire caused by bad spark plugs, the remedy is to replace the faulty spark plugs.

However, if the vehicle vibration is caused by any other faulty components other than engine misfire from faulty spark plugs, it would be best to identify the cause of the problem and fix it appropriately.

For instance, if the vibration comes from the tires due to improper wheel balance, uneven worn-out tires, or loose lug nuts, kindly implement the solution that corresponds with the actual cause.

If the problem is something you can handle, ensure to get the necessary components and fix the issue immediately. However, if it involves a complex operation, you may have to contact an expert auto mechanic to do the job.

How Do You Fix Car Shaking?

If your car constantly shakes, it is essential to fix it immediately before things get out of hand. Meanwhile, fixing a shaky vehicle is quite straightforward. The recommendations below will help.

Inspect and fix misfiring issues

Firstly, if the vibration experience is caused by an engine misfire due to a poor connection between the spark plug leads and the plug terminals, ensure to push the leads onto the plugs to enable them to click properly. Also, if you have any bad spark plugs, replace them immediately.

Replace Inspect and fix tire issues

Secondly, inspecting your car to determine the exact cause of the vibration is vital. One of the first areas of inspection is the wheels. If you discover the vibration is associated with an improper wheel balance, uneven tire wear, etc., kindly fix them immediately.

Replace bad engine mount

Again, if you notice sporadic vibrations from your engine caused by a broken engine mount, it would be best to replace it immediately to help stop the unpleasant vibrations.

Replace the stuck brake caliper

If you discover that your car pulls to one side or vibrates randomly when braking due to stuck brake calipers, you will need to replace the components to rectify the issue ASAP.

Fix/replace bent driveshaft and axle

If you notice that your car vibrates due to a bent driveshaft or axle, kindly replace the components after proper diagnosis. The replacement will cost quite some money. However, you can factor the cost into your repair/maintenance budget.

In any case, it is essential to carefully diagnose all suspected areas or components if your vehicle constantly vibrates before opting to replace of any components.

Should I Drive If My Car Shakes?

Driving while your car vibrates consistently is not ideal, especially if the cause of the issue is delicate. However, the vibration may not hinder the vehicle’s movement. Unfortunately, vibrations caused by tire problems are some of the major culprits in road accidents.

Also, when a car vibrates due to bad spark plugs, the engine will eventually be at risk in the long run. Therefore, driving your car irrespective of the vibrations caused by failing spark plugs will lead to severe engine problems if you fail to rectify the problem as soon as possible.

can bad spark plugs cause car to shake


A car shaking after changing spark plugs shouldn’t be a surprise, as many other faulty components can be responsible for the vibration. So, if you suspect any other culprits besides faulty spark plugs, ensure to fix them ASAP.

Meanwhile, carefully confirm if the spark plug leads click well onto the terminals. Also, ensure that the plugs are not damaged by the factory or during installation. Otherwise, you will need another replacement.


Mr. Shafiqule Islam is a graduated Mechanical Engineer and has more than 15 years experience of repairing and maintenance of different brand vehicles like Toyota, Mitsubishi, Ford, Mercedes, BMW etc. He is also giving training to Mechanics. He has started writing to share his practical knowledge to Vehicle Owners, Drivers and Mechanics to keep their cars at best fit.

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