Why Does My Car Idle Rough When I Turn On The Ac

Do you feel your car getting heavy while you turn the A/C on? This means you are getting idle rough while you turn the A/C on. You just want the cool air to flow slowly and silently when you activate the AC of your vehicle. You’re definitely not expecting that to impact the way the vehicle works. When the AC is turned on, it is not at all uncommon for the engine speed to decrease suddenly, so if the engine continues to surge up and down, or otherwise behaves as if it is about to shut down, there is something that requires consideration.


Common reasons for this to happen

There some common reasons that cause idle rough. Let’s see them in brief.

Carbon Buildup

Several engine components are exposed over time to carbon deposition, which can put a massive strain on the engine. If your AC compressor applies additional load, it causes you to miscalculate the machine and raises your idle speed too much. The IAC valve, the valve EGR, and the throttle body are typical sources of carbon buildup.

Fault in IAC Valve

Apparently, the IAC will pass the throttle plate in a limited volume of air. During the cold start of the engine, extra air improves the air-fuel mix. It helps to improve engine rpm, for example when you turn on the AC or freeze system when an additional load is put on your engine. However, the engine idle speed will increase as required with a defective or restricted IAC valve.

Dirt in the throttle body

The throttle body is mounted to the intake and controls the air quantity that the engine will meet. Often the edges of the throttle valve itself will absorb carbon over time. If the valve does not reach a completely closed position, the carbon just throws it all off the idle control system. Watch the stop screw on the throttle lever to make sure that when the accelerator is not pushed, the lever touches the screw.

If not, the throttle valve itself is expected to have a massive buildup of carbon. You can only cut out the wide air tube and clean the throttle with carbs and rags, but the throttle body has to be removed more regularly to be washed thoroughly.

Defected condenser fan

A defective refrigerant or condenser fan will raise the high pressure and abnormal idling.

When the fan has a variable rate of cooling or condensation, make sure the fan operates properly. If required, a simple test can help you conduct some fast circuit tests. Or you can solve problems with a simple refrigeration fan.

Cracks in the belt

This is a reasonable starting point because you might not have to go anywhere. The compressor air conditioning system is the engine’s largest belts. It is associated with two substantial sleeves. It can be powered by the same belt that runs everything things, or it can have its own belt.

Within that workshop guide, check the belt stress. Test the automatic tensioner operation too. For cracks or glazing, inspect the belt board. You could repair the belt or have it fixed for you if it is more than five years old.

The loose or worn strip sliding because the engine will make the air conditioning fee overcompensated.

Fault in the vacuum line

Vacuum lines are a good base for any vehicle efficiency problem. Many parts are powered by the engine vacuum which can lead to a wide range of problems if either of these lines were misrouted or leaked. Test the vacuum routings with a fitting vacuum diagram for condition checking.

Bad AC System

Sometimes all you can blame your AC system. Your AC should be able to differ up to 30° or higher in temperature. Let’s assume it’s 70° F outside turn the AC to full extend you should get 40° or less temperature in the cabin.

If this doesn’t occure get to a Car professional because AC repairing on your own is a risky business.

Over Filed Air Condition System

Since a low coolant can cause problems with your AC and engine flux, an overfilled unit can cause the same problem. The coolant has to be ‘right’ or you’ll have a lot of issues.

Fault in Idle Speed

Unless you identified the causes of the issue, you might have to change the idle rpm.

It is possible to change idle speed on older models with a carburetor. This is also performed on multiple carburetors daily.

Shift the idle velocity screw and search the idle solenoid according to your specific model. Follow the auto maintenance manual for guidance.

Frequently Asked Questions (FAQ)

Here is some Frequently Asked Question that might appear in your mind.

What does rough idle feel like?

A rough idle is generally recognized by a trembling and jumping sensation in the car. You can also note strange noises, as well as inaccurate RPM counts.

What happens if my car rough idle?

The drawbacks of a rough idle will in the coming quarters limit fuel savings and bad performance, starting troubles, or possible problems with engines.

Can rough idle damage the engine?

Car Rough Idle can definitely damage the engine in long run. If you have a car surge unknowingly that might be one of the reasons your engine breaks down suddenly.

Is idling with AC on bad?

You can let on for a long time any car idle with the AC without damage. If the cooling mechanism functions right, you can sit and let it go continuously in any modern car.

Does AC make engine hotter?

Auto air conditioning (AC) will increase the heat of the engine in the summer, creating more heat in the engine room and more tension on the engine to run the AC compressor.


Why does my car idle rough when I turn on the ac? We hope that you got all the points to identify the main reason for idle roughing. Get to the sections one by one and check all the possibilities. You can either check all the points on your own. You can at least get the visual idea if you are not that professional. We absolutely recommend going to a Car service professional if you ever feel car idle rough. Yet this article should help you understand what you need to change or fix by your mechanic.

We will be happy to hear your thoughts

Leave a reply

Car Decorates