Car shakes at idle but smooths out while driving — causes and fixes

Cars develop problems as they get used over time; however, some issues can leave the driver wondering what went wrong. One such problem that confuses the driver is when the car shakes at idle but smooths out while driving. If you experience this problem, it is best to have your car checked to avoid unwanted occurrences.

It can be frustrating when your car shakes at idle but smooths out while driving, and here, we highlight some of the possible reasons why this happens and what you should do.

Why does my car shake at idle but smooths out while driving?

There are various reasons why your car shakes at idle but smooths out while driving. It could arise due to common problems like dirty spark plugs, worn-out belts, and defective engine mounts.

Dirty or faulty spark plugs

The importance of spark plugs in delivering a smooth and desirable ride quality cannot get overemphasized. Spark plugs generate the spark that assists the engine in igniting the fuel. When your spark plugs get clogged with excessive accumulation of carbon or soot, it becomes difficult to generate the needed spark to ignite the fuel.

For this reason, you will experience your car shaking and engine misfiring. Dirty or faulty spark plugs are common reasons a car shakes when idle but smooths out while driving.

Defective engine mounts

When the manufacturers’ couple vehicles, engine or motor mounts get installed to hold the engine in place. The engine mounts absorb excess vibrations and shocks that the engine may generate, so the driver does not feel uncomfortable vibrations.

However, when the engine mount is damaged, it can no longer hold the engine in place and absorb vibrations. A defective engine mount results in the vibrations or shaking you feel when your vehicle is idle but smooths out while driving. It is important to note that driving with a defective engine mount can lead to severe problems for your car, including a damaged engine.

Worn out or loose belts

In addition to creating excessive noise from your vehicle, loose or worn-out belts are also a significant cause of shakings and vibrations from your car when idle. For example, the timing belt is responsible for connecting the pistons’ position with the corresponding valves.

The connection between the pistons and the corresponding valves gets compromised when the timing belt gets worn out or loose. Furthermore, the engine’s revolution gets altered, and you experience your car shaking when idle. Other belts can also cause your car to malfunction when worn out or loose.

Faulty fuel intake system

When you drive your car, different systems function all at once to ensure the vehicle’s smooth operation. The fuel intake system is one of the systems at work and includes fuel injectors. As the fuel injectors control the amount and timing of fuel going into the combustion chamber, they can get clogged due to the buildup of dirt.

When the fuel intake system is faulty due to clogged fuel injectors, the engine’s steady and constant supply gets altered, leading to your car shaking.

Disconnected or faulty vacuum hose

The vacuum hose is one part of a vehicle that doesn’t get much attention; however, it is a significant contributor to the smooth operation of any vehicle. The vacuum hose or tube is responsible for cleaning and removing exhaust gases from the engine.

When the vacuum hose gets disconnected or has an unnoticed defect, a buildup of problems can plague your vehicle’s engine. Primarily, your engine can get damaged due to exhaust gases in it. Also, due to the faulty engine, you may experience shaking and vibrations that may prove discomforting.

Faulty air intake system

The air intake system functions accurately with the help of an airflow sensor. The sensor measures and determines the amount of air in the car engine and relays the information to the control system. When the airflow sensor is faulty, various problems can plague your engine and cause your car to shake.

Also, the air filter can get clogged due to excess dust. When the dust still lingers, the amount of air getting to the engine is limited, and this can cause severe engine problems like overheating and cause your car to shake when idle but smooths out while driving.

Bad or failing throttle body

Modern cars have a throttle body to control the amount of air that flows into the engine. The action of the throttle body promotes optimal performance from the vehicle’s engine. When the throttle body gets faulty or clogged with dirt, the engine’s performance gets reduced, leading to the engine shaking due to the reduced amount of air getting to it.

Other problems like reduced mileage, poor acceleration, and electrical malfunctions also occur due to a bad or failing throttle body.

How to fix car shaking when idle but smooths out while driving

Drivers may get restless and defeated when they notice their car shakes when idle but smooths out while driving. However, there are possible steps to fix the problem.

Replace bad spark plugs

Driving around with faulty spark plugs can cause your engine to develop new problems. If your car shakes when idle due to faulty spark plugs, a simple fix is to have the spark plugs replaced immediately. Although, if the spark plugs aren’t damaged, you can have them cleaned using a spray-on cleaner for plugs and a wire brush to clear out the accumulation of soot on the electrode. Cleaning out plugs with excessive soot accumulation is a great way to fix the problem; however, we recommend replacing the plugs completely.

Replace engine mounts

If your car shakes when idle but smooths out while driving due to a defective engine mount, replacing the engine mount is a great way to correct the problem.

You may find that replacing the engine mounts is expensive, but leaving them unattended can cost you, even more when all of the issues develop from the defective engine mount. Consulting a professional mechanic when carrying out an engine mount replacement is vital to avoid poorly done work.

Tighten loose belts

Ensuring that all loose belts are adequately tensioned can stop your car from shaking when idle. However, in cases where the belts get completely worn out or damaged, it is preferable to have them replaced, as opting to tighten them would not help. It is best to have the replacement done by a professional to ensure you do not make any mistakes by doing it yourself.

Clean out clogged fuel and air intake systems

Several engine damage can arise due to clogged fuel and air intake systems. When sufficient air is not getting to the engine, the engine can develop severe problems, which can cause the car to shake when idle. Also, drivers should clean the fuel injectors thoroughly, and they should replace damaged ones to put an end to your vehicle shaking when idle.

Service your car regularly

Most times, cars develop problems because they do not get the proper attention required. Having your vehicle serviced regularly can help reduce the chances of developing a problem. It can also help you spot any faults or irregularities that could escalate into a severe problem.

Is it safe to drive a car that shakes when idle but smooths out while driving?

Some drivers may overlook the description of their cars shaking when idle but smooths out while driving. However, driving a car that shakes when idle is very unsafe. You may not know the problem’s severity, which could lead to fatalities and other issues. For example, if your car shakes when idle due to a defective engine mount, your engine could fall apart while you’re driving, which would not be suitable for you and the vehicle.

It is essential to consult the services of a professional mechanic when you notice anything odd about your car.

Our take 

Cars, like all machines, are bound to develop problems along the way. However, having sound knowledge of some of these problems, the reasons they occur, and significant steps to correct or fix them can save you a lot of money and time.

While the vibration may be a result of faults from air filters, spark plugs, sensors, dirty fuel injectors, hoses, or wires, an auto technician can pinpoint the cause when inspected. Most importantly, regular inspection and servicing of your car should be adopted to avoid problems.