9 Reasons Why Car Vibrates When Idle and AC Is On

Have you ever wondered car vibrates when idle and AC Is on? I want you to imagine how unbearable it can get when it is summer period, and the fans in your house are not working. It is uncomfortable, right?

Yes, that is the same thing when it comes to your car. It will be very frustrating to drive around on a hot summer when the car’s air conditioning system is not working.

Air conditioning (AC) is a vital feature of a vehicle, and it has two primary roles. The first has to do with raising the refrigerant pressure to facilitate heat transfer. In contrast, the second is concerned with creating low pressure in the evaporator to facilitate vaporization of the refrigerant and subsequent heat absorption from the car.

You might wonder why your car shakes or vibrates so much when it is idle and the AC is on? People tend to associate this with a faulty AC compressor solely. The assumption is correct, but many potential culprits may result in car vibration. The common ones include a dirty throttle body, a defective or dirty AIC valve, a faulty condenser or cooling fan, faulty engine mountings, and worn-out spark plugs.

All these will be discussed in detail below.

Why Car vibrates When Idle and AC Is On

1. Load on engine

All air conditioners need a compressor to function effectively. As for your vehicle, the car engine will trigger elements like idle speed or air control motor whenever the Ac system is turned on.

The AC compressor will put a lot of pressure on the engine because of the high-tech insulation.

When the pressure goes above a specific limit, it can be responsible for car vibrations. Such vibrations when the AC is on will usually come from turning the steering wheel.

There is a danger inherent in this. As the pressure keeps growing, it poses a risk to other car parts, which may end up breaking down – some engine parts might also wear out when the AC continuously loads the engine.

That will be very expensive in the long run as you may have to replace some parts. You should carry out regular car maintenance to remain safe and keep the load-on-engine issues at bay.

2. Faulty Ac compressor

Here is a quick snippet of how the car’s AC system operates. Once you turn on your car’s air conditioning system, the car engine sets the air control motor in motion.

As a result, the air conditioning compressor becomes more draining and raises the temperature of the refrigerant before it flows into the condenser.

What will be the consequence if the AC compressor becomes faulty? It will exert an excess load on the car engine, which will eventually lead to car vibrations when the car is idle, and the Ac is on.

Such vibrations may result in engine stalling (drag can also be caused by leaving the car engine idling for a long time). Prolonged dragging while the AC is on may exacerbate engine stalling and then further shaking.

To avert such a condition, you will have to pay more attention to the components of the AC system.

For instance, you should check to ensure that the conditioning system is not overcharged or overfilled. If you notice such, you should immediately embark on removing the Freon from your car.

Alternatively, you may want to accelerate the car when the AC is on to see if you realize a difference in the pick. A difference generally indicates the need to replace the AC system.

3. A defective fuel injector

Your car engine cannot operate optimally without a fuel injector – fuel injectors are crucial components of vehicle engines. Their task is relatively straightforward: electronically spraying fuel into the car’s engine using controlled valves.

Without fuel, the engine is as good as dead. That highlights the central role played by fuel injectors. When the injectors become faulty, they strain the car engine, and the car starts to shake when the AC system is turned on.

If you are not keen, you might never realize that there is a problem with the fuel injector. The best course of action is to do regular servicing to your car. Ensure that a professional checks the fuel injector whenever you have sought his services.

Should you find that it is damaged, you should mitigate the situation by replacing the fuel injector as soon as possible.

4. Worn out engine mounting

Almost everything we have looked at so far has something to do with the car engine. It would be impossible for your car engine to stay in place without engine mountings.

Mounts ensure that the engine and transmission are firmly held and prevent them from shaking whenever your car is in motion.

To emphasize what has been stated above, turning on the Ac system increases the load on the engine. The immediate result is that the load increases the strain on the engine mounts, and they are likely to break or become loose when they cannot withstand such pressure.

The engine will then move around when you turn the AC on, causing the vibrations you are hearing. Sometimes, you might hear the AC producing a clicking noise.

That is a pointer to the fact that the engine mounts might be loose.

To fix the issue, you have to visit an auto repair shop where you can have the engine mounts replaced.

5. Bad spark plugs

Like the other components I have already discussed, your engine will barely work if it lacks a spark plug. The engine component is responsible for producing power that starts the engine. It creates an explosion and an air/fuel mixture to achieve this.

If the spark plugs are damaged, you will hear your car engine vibrating when the car is idle, and the Ac is turned on. The only solution to such a problem is replacing the spark plug with a new one.

6. A faulty throttle position sensor

Let me start by explaining what a throttle position sensor (TPS) is. It is a component whose role is to measure the air taken up by an engine. The throttle position sensor relies on the throttle valves to take these measurements.

The distance in which the accelerator pedal has been pushed directly influences how a throttle blade or valve is opened.

Thus, the position sensor takes the measurements by monitoring the movements of the throttle valves.

However, the position sensor is not able to control the revolutions per minute (RPM).

Where the sensors are faulty, the RPMs will not remain constant after you have turned on the AC system. The unstable RPMs can then cause your car to vibrate when idle and the AC is on.

To avoid the vibrations, you will have to replace the throttle position sensor or fix it if the damage is minor.

7. A dirty throttle

It is a car part located between the air cleaner and the engine’s intake manifold. From its location, you can easily decipher that it plays a vital role – it is an air-passing component responsible for maintaining the airflow system in the car engine.

When the body of the throttle gets dirty, it prevents the flow of air into the engine. An insufficient air supply causes your car to vibrate when the AC is turned on, and the vehicle is idle.

Fortunately, this problem is easier to fix and IS also cheaper. You don’t have to buy new parts for replacement. Instead, you have to clean the dirty throttle body, and voila! There will be no more car shakes.

8.A faulty mass airflow sensor

A faulty mass air flow sensor could be another potential culprit that makes your car vibrate when the AC is on, and the vehicle is idle.

A faulty mass airflow sensor may be attributed to other factors. As a point in case, the engine and the AC compressor of your car usually exert high pressure on the mass airflow sensor to blow cold air.

The pressure may result in damage, and the car becomes shaky. It would be best if you regularly had the sensor checked up when y0u visit an auto repair shop to ensure that it is working well.

9. Loose or disconnected hoses

Hoses form part of the car’s air conditioning system. They are the weakest components of the Ac system since they are made from flexible rubber.

That means that they are bound to break or become loose from time to time.

When this happens, the hoses may get separated from the engine mounts, which are supposed to hold them in place and remain firm. They will then lead to the production of shaky or vibrating sounds whenever the car is idle, and the AC is turned on.

On Why Car Vibrates When Idle and AC Is On

While the main thing why your car vibrates when idle and the AC is on is a faulty AC compressor, this is not the sole reason your car might behave so.

There are other potential factors that you should investigate. These include a load on the engine, a defective fuel injector, worn-out engine mountings, bad spark plugs, a faulty throttle position sensor, a dirty throttle body, a faulty mass airflow sensor, and a faulty mass airflow sensor loose or disconnected hoses.

I have explained in detail each of these factors. I hope that you found this information useful!