Car trouble is always a worry since they are an indispensable part of our life. If your car is shaking up when left idle, stopping or when the air conditioner is on, we have some possible reasons for you. Take a look at our full guide below.
10 reasons a car vibrates or shakes
There could be many reasons for this, including a tire or a suspension problem. The brake rotors could have an issue. The spark plug could be faulty, or the transmission fluid could be low.
We look at all the possible causes and the symptoms that will show up to spot them. First, you must realize when the car is shaking or vibrating when idling, stopped, or the AC is on. It could be when it is running idle, when the air conditioner is turned on, or when it’s stopped.
Summary
The most common reason why a car vibrates or shakes when idle is a faulty spark plug. This happens because dirt and carbon builds up on the component, which may cause the engine to misfire.
Other reasons include:
- Disconnected vacuum hose
- Worn out brake rotors
- Faulty AC compressor
When idle or stopped.
A car is idle when the engine is running, but the vehicle isn’t moving. If you are facing issues like shaking or vibrations when idling in traffic, here are some possible reasons for this.
1. Faulty spark plug
A spark plug is a small but crucial part of any 4-wheeler. It is what prompts the air and fuel mixture to be ignited. Thus it powers the whole 4-wheeler.
Since they are used every time you power up your car, there can be some carbon and dirt build-up that may obstruct its working over time. It may cause the engine to misfire and thus shake when the car is idling.
| Reason | Explanation |
| Carbon Buildup | A buildup of carbon on the electrode can interfere with the spark. |
| Electrode Erosion | The electrode can erode. It happens due to exposure to high heat and pressure. |
| Oil Contamination | Oil can seep into the spark plug well. It may cause a misfire. |
| Overheating | The spark plug can become overheated. It becomes damaged due to a lack of proper cooling. |
| Vibration Damage | The spark plug can become loose and damaged due to engine vibration. |
| Wear and Tear | Over time, the electrode can wear down. It results in the gap between the electrode and the center electrode becoming too wide. |
It shakes when starting, then runs fine.
It is another faulty spark plug or air/fuel mixture symptom. Since the spark plug is primarily responsible for starting the 4-wheeler, it can result in tremors when starting. As you drive on, the shaking goes away. However, that doesn’t mean you shouldn’t get your vehicle checked. Go to a professional and get the repair work done pronto!
2. Disconnected vacuum hose
All parts of an engine work in tandem. When this tandem is disturbed, the symptoms will appear in your 4-wheeler in several ways. One of these symptoms is vibrating. The spark plug and air-fuel mixture are ignited once enough pressure is generated through the vacuum hose.
Thus if there is a leakage in the hose or the hose disconnects while driving, there won’t be enough pressure to power up the car.
It can ultimately lead to the tremors you feel. Here is another symptom that the vacuum hose is malfunctioning:
At slow speeds.
Adequate pressure is one of the most crucial things in the smooth running of a vehicle. Suppose you feel shaking when idle and especially at slow speeds. It could be a sign that the vacuum hose has a leakage.
Suppose the vacuum hose comes undone and is no longer attached. In that case, enough air pressure is not generated for the smooth running of your baby.
Vibration at slow speeds is natural until the leakage is fixed or a new hose is installed.
3. Brake rotors are worn out.
The job of the brake rotors is to absorb friction in the tires. The more quickly this happens, the easier it is to come to a halt when you press the brake.
Over time, the rotors may get damaged or worn out. It results in a longer stopping time. The car shudders in the steering wheel as well as the pedal. It will let you know that it’s time to get the brake rotors checked out and replaced.
Another symptom apart from shaking is the screeching sound you will hear once you stop the 4-wheeler. It can be a variation of growling and grunting that is hard to miss. Here is a common symptom that something is wrong with the rotors:
Jumping when stopped.
If you experience a lurch or jump when stopping the car, perhaps at a stop light, it could be an issue with the clutch plate or the brake rotors. If you have examined the clutch, it is worth checking out the brake rotors for any issues. When friction is reduced, it could mean the brake rotors have worn out and are not performing to their best capacity.
4. Loose engine and transmission mount
Engine and transmission mounts are very important to the working of an engine. They are primarily responsible for absorbing and isolating a car engine’s vibrations while running. If this part is out of sync, it will lead to more vibrations in your car than usual.
It will need to be repaired or replaced as soon as possible. The smooth functioning of the engine is impossible without the tremors being redirected and absorbed.
Here are some more symptoms of the same:
In drive mode but not in neutral.
Your car doesn’t vibrate when positioned at neutral gear because the transmission mount is not engaged at that moment. A car in neutral mode also doesn’t require any power and gives no power to the wheels. That’s why it will vibrate in the drive but not neutral.
5. Worn-out suspension and joints
You must be familiar with a ball and socket joint that holds your legs in place and allows flexible movement. A car’s wheel and suspension must also move in sync in the same way. It is enabled with a ball joint. A loose or damaged ball joint will cause your entire car and your steering wheel to shake.
What to know about worn-out suspension and joints:
- You should not drive.
- The joints are part of the steering suspension. If you drive, you could lose control.
- You’ll pay upward of $150 to fix ball joints.
It will also lead to impairment of the alignment of your vehicle. Therefore, getting your joints and tie rods is super important to get the shaky feeling away! Here are more symptoms of the same:
The steering wheel shakes when sitting still.
If you’ve just stopped at a stop light and noticed that your hands are in vibrate mode, it could be due to a worn-out ball joint or suspension. Just as your legs shake if you’re trying to walk on painful joints, the car also shakes when the suspension or tires are off balance.
The suspension must be checked every time you get your car serviced.
When the AC is on.
Your car may be driving around smoothly until the Air conditioner is turned on. Once this happens, you might feel like you have unleashed a monster. Here are some reasons why this might be happening.
6. The AC compressor is faulty.
Like in your home, the car’s air conditioner also has a compressor. The job of the compressor is to pump refrigerant into the car system. The air control motor also starts up when the AC is turned on. Together they work to produce cool air inside the car.
If this part becomes faulty or damaged, it can lead to more load on the engine than desired.
Eventually, this will cause the car to shake and the engine to heat up. Avoid this by checking the compressor every time you get your car serviced.
7. Dirty throttle
This component enables the passing and circulation of air for the AC system to work. Over time it is natural for it to accumulate dirt and carbon build-up that can disturb its proper functioning. When the system isn’t finding enough air to circulate, it will result in the car shaking and screeching.
That is why it’s important to clean these parts as part of regular servicing from time to time.
8. Faulty fuel injector
The fuel injector does exactly what it sounds like. Its job is to disperse fuel into the system at controlled speeds. If it stops doing this, there will come a time when the fuel is missed entirely and not supplied.
It causes the engine to backfire and shows up in many different ways in the car. The most frequent symptom is idling when the car AC is turned on. When the car is idling, it might shake, or the check engine light may come on.
You can also check for the smell of fuel lingering in the air or any fuel leakage behind the car.
Here is another symptom of the same:
The engine was running rough and shaking.
Suppose your engine is growling like a beast and shaking up the vehicle. It’s likely a fuel issue. Whether it’s to do with the spark plug, motor shaking, or the fuel injector, all reasons will cause your engine to act like an awakened beast.
9. The throttle position sensor is malfunctioning.
The throttle position sensor has an important job. It has to ensure enough air is being taken in for it to mix with the fuel and create an optimum air-fuel mixture. The sensor keeps track of how far the valve can be opened to let in the air, which is proportionate to how far the gas pedal has been pushed.
If this sensor is not working, it can lead to fewer rotations per minute of the tire. On top of that, the engine will take on too much load if the AC is turned on. It leads to car shudders.
10. A bad catalytic converter
Less exhaust can escape if your catalytic converter is bad, which can cause it to rough idle. Even if it’s an expensive part of the car, it’s better to get it replaced if you notice this behavior.
A bad catalytic converter will eventually damage your engine if you drive extended distances.
Here’s a look at the associated cost.
| Issue | Cost (approximate) |
| AC compressor faulty | $500 – $1000 |
| Bad catalytic converter | $500 – $1000 |
| Brake rotors are worn out | $200 – $400 |
| Dirty throttle | $50 – $100 |
| Disconnected vacuum hose | $50 – $100 |
| Faulty fuel injector | $100 – $200 |
| Faulty spark plug | $100 – $200 |
| Loose engine and transmission mount | $500 – $1000 |
| Throttle position sensor malfunctioned | $100 – $200 |
| Worn-out suspension and joints | $500 – $1000 |
