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This Is Why Your Car Shakes While Idle but Smooths Out While Driving

What happens when a car’s ignition is twisted? It starts up and elicits soft hums from the engine, indicating that the vehicle is almost ready to be moved. These hums are normal; you can even leave the car running so that oil circulates and the engine warms up enough to be used. After this, you shift the gear and step on the accelerator, taking the car from idle and putting it in motion.

What happens when the car makes rough noises, vibrating strangely instead of giving the slow, steady, and quiet hum that should be normal? One thing is for sure in that scenario; there is a problem somewhere, and you need to locate it asap so your car doesn’t break down on the road and you have to spend exorbitant amounts of money on diagnostic and repairs.

In the spirit of exploring this phenomenon further, some issues could cause the said problem.

Below is a list of possible causes that might cause your car to shake while idling but disappears when driving. Keep in mind that the prices to fix the issue will vary depending on the model. Being familiar with DIY will help you knock off a couple of hundreds.

IssueEstimated repair cost
Worn car mounts$300-$600
Cracked coil packs$200-$350
Faulty spark plugs$100-$270
Defective idle speed control$150-$400
Defective fuel intake system$250-$400
Misfire$50-$500
Clogged air filter$30-$80
All costs are estimates and will significantly vary based on the car model and whether you can fix the problem yourself or need to take it to a mechanic.

1. Your Car Mounts Are Loose or Worn Out

This should be your first and foremost suspect, mainly because most other potential problems that cause idle shaking result in a decreased power output while this one does not. Think of your car mounts as the straps on your briefcase; they keep the contents stable and secure even though you swing it all over.

Your mounts prevent the engine from vibrating excessively, securing it in place. Ordinarily, when you drive, the engine propels your car forward through the connection to the gearbox, and the mounts keep your engine secured to the vehicle.

When your mounts are bad, the engine vibration is not dampened by the usual effect of the mounts. When driving, you wouldn’t feel this because the motion superimposes, and the car feels normal.

You can diagnose bad mounts by putting your car in neutral during idle. If the car vibrations stop, then it is a mount problem.

Related content: Why does my car shake after an oil change?

2. Cracked Coil Packs

Cracked coil packs can result from heat damage or voltage overload (caused by faulty spark plugs). Coils are typically used to transmit and convert the low current from car batteries to enough juice to fire the car by combustion.

A bad coil has many symptoms but can manifest as rough vibrations during idling. The faulty coil will not have enough power to push the specific threshold voltage to the spark plugs.

You would have to replace the coil before you can see any changes. New coils replacement presently goes for around $200 to $350.

3. Faulty Spark Plugs

Spark plugs are the small electrodes that form the high-voltage electric spark that would give enough juice to start the engine’s combustion. All cars have a set of spark plugs, and the proper functioning of all of them is necessary for the starting of the vehicle.

When any of the spark plugs become dirty, melted, or worn out, the voltage transformation system becomes inefficient; the voltage weakens, and the spark plugs would not be able to ignite the fuel in the cylinders efficiently. This manifests in the engine as misfiring or might cause the engine to shake when it is idle.

Related content: Why would a car run better with the mass air flow sensor unplugged?

4. Defective Idle Speed Control or Throttle Body

The idle speed control prevents the engine from dragging when idle. The system is designed to keep the engine running as low as possible while still running effectively without stalling when energy-consuming features are turned on. Therefore, if this system is defective, the engine stalls resulting in noticeable vibration.

5. The Malfunctioning Fuel Intake System

A faulty fuel intake system can indeed make your car shake when idle. Vehicles need a supply of fuel to move and function properly; hence, the car reacts to this if the fuel supply is inhibited or obstructed by specific factors.

The fuel systems of most cars are mostly dirty rather than bad. The accumulated dirt and debris choke the valve which delivers fuel and causes the vehicle to shake when idle.

6. Misfire

Another common cause of idle shaking of the car is a misfire, resulting in a noticeable drop in power while idle and in motion.

You might now wonder what might be the cause of an engine misfiring. There are numerous causes, including injector problems, ignition coils, spark plugs, and the absence of compression.

Fixing a misfiring engine can cost you as little as $10 to replace a bad spark plug, up to a couple of thousand for fixing a bad engine piston.

Related content: How Can A Bad Battery Cause A Car To Misfire?

7. Clogged Air Filter

The air filter of your car ensures the proper circulation of air. Hence, if your air filter is clogged with dirt, its purpose is defeated.

The amount of air making way to the combustion chamber is reduced, and the car responds by shaking excessively.

Ways to Handle These Issues

If your car is experiencing idle vibration, you might want to track down the reason for this. After the source is tracked, there are two courses of action left to be taken. These are;

Clean out the source

If the source of the problem is a dirty component or part, it should be cleaned following the car’s service manual. If you do not have experience cleaning your car’s parts, you might seek the advice or help of a professional mechanic.

Repair or replace faulty parts

If the root of the idle vibration is a faulty component, you might consider repairing that part. If a repair is not sufficient to fix the part, you might decide to replace it instead.

Related content: Why does my car die when put in gear?

Is It Normal for a Car to Shake a Little at Idle?

No, it’s not normal for a car to shake a little at idle. If your vehicle is shaking at idle, it could be due to several different issues. It could be something as simple as an issue with your spark plugs or something more severe like engine misfiring. If your car is shaking at idle, it’s best to take it to a mechanic to have it checked out.

Bottomline

If you know a thing or two about your car, you should first check and clean your car’s components. This will help you identify any blockages in the air filter that might cause your car to behave like this.

If your car keeps vibrating while idling, one should not despair and could always ask a mechanic to inspect the vehicle and come back with a quote. A car technician will have the tools and expertise that most drives don’t. And sometimes, it is a lot easier to have a professional take care of your car.