10 reasons a car vibrates or shakes when idle, stopped, or AC is on

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.

Why does my car shake?

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.

Table of Contents

Reasons a car vibrates or shakes 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

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.

ReasonExplanation
Carbon BuildupA buildup of carbon on the electrode can interfere with the spark.
Electrode ErosionThe electrode can erode. It happens due to exposure to high heat and pressure.
Oil ContaminationOil can seep into the spark plug well. It may cause a misfire.
OverheatingThe spark plug can become overheated. It becomes damaged due to a lack of proper cooling.
Vibration DamageThe spark plug can become loose and damaged due to engine vibration.
Wear and TearOver time, the electrode can wear down. It results in the gap between the electrode and the center electrode becoming too wide.

The car 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:

My car shakes when idle and driving 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.

brake rotor

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:

Car 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

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:

The car vibrates 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

Suspension for car

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.

Reasons a car vibrates or shakes when 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.

Ac compressor car

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

Holley Throttle Body

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

fuel injectors

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

catalytic converter for Audi A4

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.

IssueCost (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

Check engine light on and car shaking when stopped. What should I do?

Is your 4-wheeler rocking back and forth when stopped? It might be signs of an engine misfire.

It is a dangerous event and requires immediate attention. Here are some things you can do if you know your way around an engine.

Whether a big vehicle like a truck or a small Chevy, you can use this guide for all 4-wheelers:

Check the spark plug.

The first thing to do is to check the spark plug. Open up the engine and check which cylinder is misfiring. Disconnect the spark plug from that cylinder. Get a spark plug socket and use it to remove the spark plug entirely to take a closer look.

Once you examine the plug, you can tell the cause of the misfire. Here is what to look for:

  • The fuel regulator has malfunctioned if your plug is soaked in oil or gasoline. It needs immediate professional attention.
  • The wire that connects it to the ignition coil might be broken and needs replacing.
  • The plug is covered in black soot. It means there was too much fuel, and the engine was running rich.

Test the coil pack

The ignition coil connected to the spark plug is responsible for powering up the vehicle. If this coil is faulty, it can cause a misfire.

Test it out by removing the wire from the spark plug and connecting it to an Ohmmeter instead. Check and compare your vehicle model’s resistance with the normal resistance range. If it doesn’t match, the coil needs replacing. It’s not the spark plug that has problems.

Compression failure

It could be that overall compression is not taking place properly. For this, you can run a simple compression test of the:

  • fuel
  • spark
  • and air for each cylinder.

Remove the fuse of the fuel pump. Remove the spark plug and put a compression gauge there instead. Let the engine turn over a couple of times by starting the car. Write down the highest figure with each reading of every cylinder.

After testing each cylinder, compare the figures. All the cylinders should be in the same range. But if two are particularly low and are also right next to each other, you have found your problem!

It is where the head gasket needs replacing. Remove the cylinder head and replace the head gasket because it has gone bad and led to low compression levels.

If the cylinders have around about the same reading, the problem is not compression. Rather you should follow the next step below.

Call a professional mechanic.

Suppose you cannot find a faulty spark plug, bad coil pack, or compression issues. In that case, it is time to ask for a professional’s opinion. Don’t think there is anything wrong with the 4-wheeler, and keep driving! Rather call a mechanic before you get stranded with a breakdown.

FAQ

Let’s answer some of those burning questions about misfires and shaking.

Will a tune-up stop my car from shaking?

Yes! Servicing should ideally be taking place after every 10000 to 12000 miles. You can also make it a point to go annually. But if this is not happening, the vehicle might start to show some indication that it’s time for a tune-up. One of these is less fuel mileage. The others include shaking in a park and vibrating when idle or when stopping. It can also be weird screeching noises or grumbling. If you’re having trouble starting or stopping, it is best to go in for a service.

Should I be worried if my car is vibrating?

A little vibration is normal. There is vibration while the gears are shifting, especially in a stick-shift car. As long as the vibration is not distracting you or becoming an obstruction in driving, it is nothing to worry about. But if you find your steering wheel shuddering violently when idle and the car not stopping unless it jumps first, you must take action.

Why does my car shake on cold starts?

There could be quite a few reasons for this. A faulty plug or fuel injector could be the reason. A dirty throttle is also a likely reason. Check for adequate pressure as well as compression. Engine and transmission mounts must also be checked as it is their job to absorb the vibrations across the engine.

Is it normal for a car to shake a little at idle?

It is not normal if your vehicle is always shaking at idle or parked. A little rumbling usually occurs during the transmission of gears, but that is minimal. Vibrating all the time when idle is a sign of a deeper fault. Check spark plugs, compression, engine mounts, rotor brakes, air control valve, and ignition coils for the exact cause.

Is it safe to drive when your car is shaking?

No, it is certainly not safe. You should pull and check out the engine, especially if the check engine light is on. If you know your way around the engine, look at the mounts, the spark plug, the tire pressure, the compression in the cylinders, and the ignition coil.