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How to Fix Rough Idle When Ac Is On? (Explained)

Idling means the car malfunction in some specific area. Idling will make the driving experience rough as the RPMs might fall below 600 RPM which is typically standard for your vehicle. 

Also, symptoms will appear when you start the car, as well as abnormalities in engine temperature. In this article, we will discuss rough idle when the engine is on.

Can ac cause rough idle? 

Sometimes, an air conditioner can cause rough idle. Rough idle is considered when the car feels a little bit shaky or late responsive when driving. This might cause due to different types of reasons.

The engine serpentine belt which is used to run the air conditioner compressor requires energy from the engine to keep it operational.

But a faulty air conditioner compressor that has not been maintained over a long time might cause rough idle and shake the engine due to pressure on it.

If the air conditioner fails to function, it will put a strain on the engine and the car might shake when stopped and the air conditioner turned on.

Sometimes, rough idle due to an air conditioner malfunction might cause a long-term and excessive drag as well as engine stalling. So, you need to diagnose the issue as soon as you notice it to avoid long-term damage to your car.

How to fix rough idle when ac is on? 

Usually, a rough idle is caused by a dirty system component, such as throttle body, IAC valve, or cooling condenser fan. You can fix the rough idle by turning the key on, then slowly pressing the accelerator and spraying the throttle body cleaner on a rag, and using it to clean the throttle blade. 

Rough idle is considered when the car’s system components do not function properly or do not perform at their optimum performance. So, avoiding the issue might cause you long-term damage to your car and engine components.

A car shakes at idle when ac is on. Rough idle is considered one of the most irritating problems you might face. As a result, it might cause your car reduced fuel economy, poor performance and most importantly starting problems.

Another thing that causes rough idle is a bad throttle position sensor. Its job is to keep a note regarding the engine’s air intake. A bad throttle position sensor cannot control your vehicle’s RPM, so the RPM cannot maintain its consistency when the AC is turned on.

As a result, your car starts to shake. The following discussion is a solution on how to fix rough idle when the air conditioner is on: 

Turn off the car engine and turn the key to ON:

Once you determine that your car has rough idle, it’s time to inspect the issue. Begin with shutting down the engine and inspecting the throttle body, but keep the key to turn ON. 

Press the gas pedal slowly:

Once you are done with inspecting, get the assistance of someone and ask them to press the gas pedal slowly. You should take care when doing this, even a small mistake can cause bigger damage. 

Use a cloth to clean the throttle body:

Now, it’s time to clean the throttle body. So, when the gas pedal is being pressed, spray the throttle body cleaner onto a piece of cloth and use it to clean and reposition the bore and blade.

What causes rough idle when ac is on? 

Rough idle is caused by defective fuel injector, excess load over the engine, damaged spark plugs, or even faulty ac compressor. Faulty ac compressor leads to serious engine-related issues such as excessive drag.

If too much drag is produced when the air conditioner is turned on, it might cause the car to more stalling.

On the other hand, these issues might cause an unexpected shut down to your car in the worst cases. Some of the reasons why rough idle is caused when the AC is on mentioned below: 

A defective fuel pump:

As mentioned earlier, rough idle could be caused by different reasons and this could lead to your engine components failure. So, a defective fuel pump can be a reason why your car is on rough idle.

Since, the fuel pump filters the contaminants from the gasoline, a faulty or clogged one won’t be able to filter it and due to lack of fuel supply, the car might stall unexpectedly. 

Low battery:

Battery keeps your car’s electric components functioning properly. So, a low battery might cause an imbalance in your car’s electrical power supply system.

As a result, turning on the air conditioner will affect the car by putting extra load on it. So, low battery is another reason why you have a rough idle issue.

Damaged air compressor:

Most of the air supply system-related systems cause rough idle when the ac is on. A damaged air compressor is also one of them.

It will interfere with the engine’s operation when the air conditioner is turned on because it needs a lot of power to operate. But the air compressor won’t be able to supply that much power into the compressor.

Dirty throttle body:

Another reason why your car might be facing rough idle when the air conditioner is turned on is that the throttle body is dirty.

In case the throttle body is full of accumulated carbon as dirt, it will put excess pressure on the engine and cause rough idle when the air conditioner is turned on.

Damaged IAC:

IAC, also known as idle air control valve is one of the vital parts of the engine that causes rough idle when damaged.

IAC uses a motor to provide air to the components of the engine and the air conditioner is one of the biggest electrical loads the IAC has to control.

So, a damaged IAC will be unable to provide its service to the air conditioner and cause the engine rough idle. The easiest way to get this issue fix is to diagnose it and repair it with the assistance of a professional automobile mechanic.

You must remember a small mistake might cause serious damage to the vital engine components and cause your car engine to shake and vibrate unexpectedly.

Can a bad ac compressor cause rough idle? 

A bad air conditioner compressor can cause rough idle. It mostly interferes with the power system of a car’s air conditioning system. The job of the ac compressor is to pressurize the refrigerant into the gaseous matter and pass it to the condenser.

It is a vital part of your car’s cooling system. So, a faulty air compressor is disturbing the normal functionality of an air conditioner compressor to cause rough idle.

Although you can drive with a bad ac compressor, still it is recommended to diagnose and repair the issue.

What is normal idle RPM for a car with AC on? 

Nowadays in the cases of modern cars, they are so technologically advanced that their computerized automatic system can adjust the RPM automatically by synchronizing with the engine computer to compensate for the extra drag of the air conditioner compressor.

But, in general, it takes around 700 to 900 RPM which is considered normal idle for a car with the air conditioner turned on.

Is it bad to idle a car with AC on? 

Although it is not recommended to idle a car with the air conditioner working properly, you should avoid doing this. As long as the cooling systems of your car are functioning properly, you can simply let your car idle with the air conditioner on for a certain time.

It will cause no harm but in long run, it might cause damage to the engine components and cause you time-consuming and expensive repairs. So, try to maintain the operation of the air conditioner when idle to prevent any unexpected shut down of your car.

What causes rough idle when ac is off? 

The air conditioner is not the only culprit which might lead your car to rough idle. It could occur even if your car’s air conditioner is turned off. Because some other car components might cause your engine to rough idle even when the ac is turned off.

The list includes fuel pump failure, damage to the mass airflow sensor, a leaking head gasket, a low battery, an idle air control valve, throttle valve, evaporative emission control systems, etc.

So, when you notice the issues of rough idle, do not wait or keep driving with the issue remaining in your car. Immediately repair the issue with the help of a professionally expert automobile mechanic.

Final Thoughts 

Generally, the rough idle is caused when the inner components of the engine get damaged or defected. You might feel shaky when driving. So, whenever you notice the symptoms, immediately check the problems and better take it to an automobile mechanic to get the issue repaired.