Car Sputters When AC Is On – 9 problems and fixes – 2023

Nothing is more annoying than turning on your car’s air conditioning (AC) to find a rough and sputtering engine. Your car may sputter when the AC is on for various reasons, from small problems to more significant failures.

A worn AC compressor belt can slip, straining the engine and AC. Replacing it restores smooth operation and improves AC performance.

In this article, we will delve into the common causes of this problem and provide detailed fixes for each.

Why Does My Car Sputter When The AC Is On? How To Fix It?

1. Faulty Or Dirty Idle Air Control (IAC) Valve:

You may have a failing idle air control. The valve that controls idle air is in charge of keeping your engine’s idle speed under control. When the AC is turned on, your IAC (idle air control valve) is dirty and sluggish when responding. If this valve develops a problem or becomes blocked, it may be difficult to maintain the proper idle speed, resulting in sputtering.

Faulty Or Dirty Idle Air Control (IAC) Valve
source:mechanic base

How To Fix:
Start by reviewing your car’s handbook for instructions on accessing the IAC valve if an issue results in sputtering when the AC is on. The valve should be taken apart and cleaned using the proper cleaner.

Consider replacing the IAC valve with a new one compatible with the make and model of your car if cleaning doesn’t enhance performance. Reattach the valve, making sure the connection is secure.

At the end, run the engine, turn on the air conditioning, and check whether the sputtering has stopped.

Consult a specialist for additional diagnosis and possible replacement if the problem continues. Sputtering will be eliminated, and consistent idle speed will be restored if the IAC valve operates properly.

2. Overfilled AC System:

An overfilled AC system is one of the main causes of a sputtering engine when the AC is on. A pressure imbalance in the system due to excessive refrigerant levels may result in unpredictable engine behavior. The compressor may become flooded with extra refrigerant, interfering with its smooth performance.

Overfilled AC System
source:hydraulic suspension

How To Fix:
An overfilled AC system can be fixed by carefully recovering the extra refrigerant with the aid of a recovery machine and manifold gauge set.

The excess refrigerant should be drained by finding the low-pressure service port, connecting the recovery device, and doing so. Verify the pressure readings to make sure they fall within the recommended range. 

Add the appropriate amount of refrigerant to your vehicle’s specifications if necessary. Start the engine, turn on the air conditioning, and watch for smooth operation.

If doubtful, get expert help for a comprehensive examination and adjustment. Restoring system balance and preventing engine sputtering with the AC on will result from properly handling overfilling.

3. Carbon Buildup:

When the AC is turned on, carbon buildup on the throttle body and intake valves might interfere with the optimum airflow and fuel mixture, causing rough idling.

 Carbon Buildup

How To Fix:
Start by disconnecting the battery to ensure safety during the cleaning procedure and to counteract carbon buildup that results in rough idling while the AC is on.

Find the intake valves and throttle body, typically close to the engine’s air intake. Use a good carbon cleaner and a soft cloth to gently remove the carbon buildup from these components.

Be thorough while taking care not to harm any weak parts. Start the engine, reconnect the battery, and turn on the air conditioning. However, the problem has been resolved if the harsh idling has improved.

Regular upkeep, such as utilizing fuel additives meant to eliminate carbon buildup, can avert future instances and keep engines performing at their best.

4. Bad Belt:

It is due to a worn compressor belt and an often-ignored factor that causes the car to spike when the AC is turned on. When the belt is smooth or stretched, it may slip.

Bad Belt
source:car insurance

The compressor puts a load on the engine and the AC system accordingly. Surges are typically eliminated, and improved performance is guaranteed with an AC belt replacement.

How To Fix: 
When the AC is turned on, sputtering and noise are caused by a worn, damaged, or loose serpentine belt, which requires inspection and replacement. To find the belt and tensioner:

  1. Start by consulting the owner’s manual for your car.
  2. Look closely for any evidence of wear, cracking, or other damage to the belt.
  3. Get a replacement belt if it is worn out or damaged.
  4. Remove the old belt using the tensioner, release the tension, and then insert the new belt using the proper routing.
  5. Make sure the belt is positioned correctly on each pulley.
  6. As directed by the manufacturer, engage the tensioner.
  7. Start the engine, turn on the air conditioning, and listen for quieter operation. The belt replacement will fix the problem and stop the sputtering.

5. Dirty Throttle Body:

When the AC is on, sputtering occurs because the throttle body is dirty and causes obstruction of airflow, which alters the proper air-fuel mixture. It can be cleaned to restore engine and airflow efficiency.

Dirty Throttle Body

How To Fix:
Use these procedures for efficient cleaning to prevent sputtering from a filthy throttle body. For safety’s sake, unplug the battery first.

Find the throttle body, which is typically a part of the air intake system. Use a soft cloth and throttle body cleaner to gently clean the carbon and grime buildup from the throttle plate and bore. 

To avoid injury, refrain from exerting excessive force. Start the car, turn on the AC, and reconnect the battery. You can tell if you’ve solved the problem if the sputtering stops.

So, consistent airflow will be ensured by routine upkeep and cleaning, minimizing potential disruptions in the air-fuel mixture and sustaining engine performance.

6. Bad AC Cycling Switch:

The AC cycling switch manages the engagement and disengagement of the compressor. The compressor may cycle quickly due to a broken switch, impacting engine performance.

Bad AC Cycling Switch
source:mechanic base

How To Fix:
Replacing a broken AC cycling switch is necessary to get the compressor to engage properly. To begin with, look in your car’s manual to find the switch, which is often close to the parts of the AC system. Remove the defective switch while safely disconnecting the electrical connectors.

Install a new AC cycling switch that complies with the requirements of your car. The electrical connectors should be properly aligned before being reconnected. 

Start the engine, turn on the air conditioning, and monitor the compressor’s cycle actions. The engine’s performance should be steady if the switch replacement has fixed the quick cycle problem.

On the other hand, consult a trained technician for a more thorough analysis and assistance if the issue needs to be clarified or continues.

7. Failing AC Compressor/Low Refrigerant:

Low refrigerant levels or a faulty AC compressor can strain the engine, causing rough idling and sputtering.

Failing AC Compressor/Low Refrigerant
source:car from japan

How To Fix: 
A dual strategy is necessary to address problems caused by a failed AC compressor or low refrigerant. First, have the compressor’s condition evaluated by a qualified mechanic.

Replacement may be required if proven faulty to guarantee good AC operation and engine performance. Second, low refrigerant levels necessitate a refill according to manufacturer recommendations.

A mechanic will correctly vacuum the system, safely remove residual refrigerant, and recharge it with the required volume. Start the engine, turn on the AC, and check for improved idling and smoother operation after you’ve finished these instructions. So, the engine will experience less stress and eliminate sputtering if both issues are resolved.

8. Adjust Idle Speed:

You might need to change your idle speed if you still need help figuring out what’s wrong. On older cars with carburetors, the idle speed is adjustable. Numerous carburetors frequently carry out this process.

Adjust Idle Speed
source:mechanic base

How To Fix: 
Consult your vehicle’s manual for instructions on modifying the idle speed if you’re experiencing sputtering due to an inappropriate idle speed. The idle speed adjustment screw is typically located close to the throttle body.

Start the engine, then give it some time to warm up. Including the AC, turn off all accessories. To get the suggested idle RPM, gently crank the adjustment screw as the manual directs. 

Once everything is set, turn on the air conditioning and see the engine in action. You’ve solved the problem if the sputtering has lessened and the idle is stable. Consult a qualified mechanic for additional advice if problems persist or if doubt develops about the ability to guarantee precise adjustments.

9. Problems With The Distributor And Ignition:

Misfiring and rough idling when the air conditioner is running, might be caused by problems with the distributor and ignition system.

Problems With The Distributor And Ignition
source:mechanic base

How To Fix: 
An all-encompassing strategy is needed to address misfiring and harsh idling brought on by issues with the distributor and ignition system. Start by looking for wear, corrosion, or damage on the distributor cap, rotor, spark plugs, and ignition wires.

Any components that show problems should be replaced. According to the manufacturer’s recommendations, check and adjust the ignition timing. 

Ensure the ignition wires are connected correctly, and keep the terminals clean. If the issue continues, consult a qualified mechanic for further diagnostics and probable distributor component replacements.

If distributor and ignition problems are properly resolved, misfiring and harsh idling will be eliminated, even when the AC runs.


1. Why Does My Car Stutter When I Turn On My AC?

If the fuel injector breaks down, the engine won’t receive enough fuel, reducing performance. The engine is under even greater stress while the air conditioner is on, which causes the car to start vibrating. New fuel injectors are required if this is the root of the vibrations.

2. Why Does The Car Sputter At Idle When the AC Is On?

When a car idles poorly with the air conditioning on, it could indicate that the cooling fan isn’t functioning properly, the IAC valve is broken, or the throttle body is unclean. It can be a challenging problem to comprehend if you need to become more familiar with it.


Even though a sputtering engine with the AC on can be a frustrating experience, it’s crucial to treat the problem right away to limit future damage and guarantee your car’s peak performance. You can troubleshoot and remedy the sputtering issue, enabling you to enjoy a nice and smooth ride even with the AC turned on, by comprehending the potential causes mentioned in this article and applying the suggested fixes.

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