Car Shakes When Idle? Here Are The Reasons

Car Shakes When Idle? Here Are The Reasons

If you let your car run overtime and start to feel it shake, that can be pretty concerning. If you catch your car shaking as it idles, you need to act quickly so that you may prevent any damage. So, what is the most common reason your car vibrates when idling?

The most common reason that your vehicle shakes while idle is due to dirty or old spark plugs. By taking the time to clean and check your spark plugs, you are pretty likely to solve the problem. It can also be related to loose hoses, dirty fuel intake systems, and loose belts.

Given that hiring a mechanic can be expensive, we will be going through the different ways to find out what causes a car to shake when idle. Whether it be spark plugs, fuel injectors, or engine mounts, you can determine the issue by looking at common problems.

6 Reasons Your Car Has A Rough Idle

Below is a list of common reasons that your car shakes while idling:

  1. Dirty or old spark plugs
  2. Broken or disconnected hoses
  3. Dirty fuel intake
  4. Loose, broken, or disconnected belts
  5. Broken or worn motor mounts
  6. Clogged air filters

If you plan on repairing your car yourself, always be sure to have your parking brake on and your battery disconnected. Also, if you feel your car shaking on idle, do not drive it. You may potentially increase your repair cost and put yourself in danger if you make this decision.

#1: Dirty Or Old Spark Plugs

If you have ever heard the term “not firing on all cylinders,” you might be familiar with our first suggestion. Dirty or old spark plugs are not good at holding a charge, so you need to replace or clean them.

If your car is challenging to start, that is one sign that you need to clean or replace the spark plugs. You may also notice slow acceleration, low fuel economy, and your engine misfiring.

You can find your spark plugs through connections to your engine. You should see up to eight wires, which you can remove with your hands. Be sure the engine is cool and disconnected from the battery before you do remove any wires.

If your spark plugs seem blackened, try and clean the wires with compressed air or a stiff wire brush. Dirty wires are one of the more common reasons your engine isn’t getting enough energy.

If you need to make a replacement, the owner’s manual will reference the correct measurement you require. Unless you have unique circumstances, most spark plugs can last up to 100 thousand miles.

#2: Broken Or Disconnected Hoses

The hoses that come out of your engine are typically an airtight system built to hold together. However, a vacuum hose leak can cause unwanted fumes of gases to exit your engine rapidly. As a result of this mass escape, your engine will misfire, shake, and eventually shut down.

Another sign of a faulty vacuum hose comes from a noticeable hissing sound coming from your vehicle. You may also see an abnormally high idling speed. You may also have exhaust issues, ventilation issues, and AC issues. You may also see the check engine light is on.

To fix a vacuum hose, you can use leak seal tape. However, you should consider having a mechanic look at this problem. A faulty vacuum hose can be incredibly dangerous if it finishes braking as you drive.

#3: Dirty Fuel Intake System

As your engine gets older, the buildup of dirt and age inside of the car cause clogs. Your fuel intake system is no exception to this, as you may find a disgusting buildup of sludge inside of it. You may also see similar issues if you have poorly adjusted valves, causing the fuel mixture in your engine to be off.

These issues can also extend to the fuel pump, which should be checked alongside this as you inspect your vehicle. If you see any signs of damage or age, seek out a mechanic who has experience working with fuel pumps and injection engines.

Professionals can clean your fuel injection system by following the maintenance schedule of your owner’s manual. Typically, you want to schedule these cleanings every 60 thousand miles, but your vehicle’s warranty may have a different opinion.

#4: Loose, Broken, Or Disconnected Belts

Your timing belt is the cause for a lot of concern in your engine. As your engine gets older, you can expect the age of your belts to catch up to you. Over time you can see them become cracked, aging, and worn, which means you will need to replace them.

Signs that your belts are failing also come from other functions of your car failing, such as the fans in your AC. You may also hear a loud squealing noise coming from the front of the car. In some cases, your power steering may also cease to function.

All of your belts are at the front of your vehicle, and this is one case where you can perform some DIY engine repairs. If you need help performing timing belt repairs, check out the video from AutoZone for more details:

#5: Broken Or Worn Motor Mounts

If the answer to “why is my car shaking” comes from worn engine mounts, you have a very dangerous situation. If you feel your car shake while at a stoplight, that means you need to pull over and seek assistance immediately. If your motor mounts fail as you are driving, it can result in your engine not being properly secured. This failure can cause severe injury for you and other people on the road.

One way to be sure that your car has this problem is by shifting it into neutral. If your car’s shaking reduces while it is neutral, that is a good sign you need to replace the motor mounts.

This is also something you can technically do yourself, but you need a significant amount of mechanical skill to get it done.

If you don’t have that skill, there is no shame in asking for help.

#6: Clogged Air Filters

Much like your fuel injection system, the air filters in your engine can get clogged as you wait over a long period. This simply comes from use, as there is no real way for you to prevent an air filter from being dirty. If enough time has passed since your air filter has been checked, that is a good sign that you have a rough idle.

Clogged air filters will cause the fuel mixture in your vehicle to become unbalanced. As a result, you may find this to be associated with a worse fuel economy. If it feels like you have used more gas than usual, check the filter.

To clean your air filter, you can take it out and use a combination of water and mild soap. Dip the air filter into a bucket large enough to fit it. Pull it out and rinse it, then let it dry over a short time.

How Much Do Repairs Cost?

Given all the potential issues, the cost of your car shaking when idle can be very expensive. Here is a list of different prices related to your timing belt, spark plug, and other issues that can cause car shakes:

  • The typical amount you can expect to pay for a spark plug is around $16-$100 per plug. This does not account for labor, which will add $100 to the total in most situations.
  • The cost of buying patching material for your hoses shouldn’t be more than $10. However, if the leak is located somewhere deeper in your vacuum system, the price can be up to $1000.
  • Cleaning your fuel intake system and fuel injectors should cost no more than $100. Most auto repair shops only charge around $60.
  • The cost of belts for your engine (whether they be timing or serpentine belts) should be around $25. If you include labor, the labor cost can be about $150 per belt.
  • Engine mounts by themselves cost anywhere between $50 and $150 depending on your vehicle. However, labor costs can drive this up to $800 due to the time and effort to jack up an engine and lift a car.

How Do I Get My Car Safely Home?

If you feel the steering wheel of your car shaking while idle, do not drive fast. Going too fast may damage your engine. Instead, travel at low speeds and turn on your emergency lights. These lights will inform other drivers that you are trying to get home safely. Once you get it home, keep it parked until you can fix it. Driving a car that shakes can cause previously existing issues to become more severe.


Your engine idle should be incredibly smooth under everyday situations. If it is not smooth and you can feel your car shaking, that is a sign that you need some help.

Whether it’s related to your spark plug, fuel intake system, or timing belt, your car needs to be fixed so you can get back on the road. If your car shakes when idle, it can lead to an incredibly unsafe situation.

Don’t try to drive it. Instead, begin to diagnose the potential issues among those we listed above. By following the guide and our suggested safety protocols, you will be able to increase your car’s lifespan. Choosing to drive your vehicle anyway will lead to a far more expensive fix and more time without driving.

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