What Causes Engine Shaking When Idling with AC On?

[CarolineFitz]

The reasons for engine shaking when idling with AC on are as follows: 1. The compressor pressure is too high. Excessive pressure increases the engine load, thereby affecting the vehicle's stability. 2. The throttle needs cleaning. Whether the throttle operates normally directly affects whether the engine can work properly. During vehicle operation, carbon deposits can accumulate in the throttle. Excessive carbon deposits can block the engine's normal air intake, resulting in insufficient engine power to drive the compressor or barely managing to do so. In such cases, starting the car and turning on the AC will cause the engine to shake at idle. Therefore, it's essential to check if the throttle is clean and clean it promptly if necessary. 3. The engine is too dirty. Prolonged lack of cleaning or aging can affect the engine's normal operation. In such situations, you either need to replace the engine or clean the carbon deposits inside it to ensure the vehicle runs smoothly.

[JamesRose]

I've driven quite a few cars and found that engine shaking when idling with the AC on is usually due to increased load at low RPM. When the compressor kicks in, it demands extra power. If the ignition system is aging or the spark plugs are worn out, combustion becomes less smooth, leading to increased vibration. There's also the issue of carbon buildup. The accumulated carbon deposits in the cylinders cause uneven fuel mixture, making the engine struggle and shake when the AC adds load. It's recommended to check if the spark plug gaps are normal and clean the throttle body carbon deposits. Don't overlook these details—unstable idling not only causes shaking but also wastes fuel, and in severe cases, it might damage the engine. Regular oil changes and air filter replacements can help prevent this. Avoid prolonged idling with the AC on, and it's best to visit a repair shop to diagnose the specific cause. Don't delay to prevent minor issues from turning into major problems.

[Myron]

As someone who frequently works on cars, I believe the root cause of idling with AC on causing vibrations lies in sudden load changes and system imbalance. The compressor operation is key—it directly increases engine resistance. Since idling already runs at low RPM, it easily exposes issues like faulty ignition coils or clogged fuel injectors. Once fuel supply becomes uneven, the engine shakes erratically. Unstable voltage or an aging battery can also affect AC startup stability, amplifying these abnormalities. Pay attention to the AC system's condition—insufficient refrigerant or worn compressor bearings can worsen the problem. Routine maintenance shouldn't overlook carbon deposit cleaning and wiring checks. Testing spark plugs or simply measuring fuel pressure can help detect potential issues early, preventing damage to the vehicle.

[GideonLee]

As a daily driver, experiencing shaking when idling with the AC on might be due to the engine struggling with the extra load at low RPM. When the compressor kicks in, unstable RPM can cause vibrations. Common causes include excessive carbon buildup or dirty fuel injectors, leading to incomplete fuel combustion. Minor shaking can sometimes be normal, but frequent occurrences may indicate issues with the ignition system or aging engine mounts. Don't overlook regular spark plug replacements and carbon cleaning, as these can reduce vibrations and ensure smooth, safe driving.