Why Does the Car Shake When Turning on the AC in D Gear?

[VanRuby]

When the car is in D gear and the AC is turned on, it actually increases the load on the engine, so some shaking is normal. Here are the related details: 1. Excessive Carbon Buildup: When the AC is turned on, the engine needs to generate more torque to keep the car running smoothly. However, if the shaking is particularly severe, it might be due to excessive carbon buildup from prolonged driving. 2. Turn Off the AC: After using the car's AC while driving, make sure to turn it off before parking. This way, the engine won't have to bear an extra heavy load when the car is started again.

[TylerLynn]

When I encounter shaking while the air conditioning is on and the car is in D gear, the first thing that comes to mind is the sudden increase in engine load. Once the air conditioning compressor kicks in, the engine has to work harder, especially at idle or low speeds, which can easily cause the RPM to drop and lead to body vibration. Common causes include aging or carbon-fouled spark plugs affecting ignition efficiency, or severely worn engine mounts leading to failed damping. My own car shook like this last time, and upon inspection, the spark plugs were found to be heavily eroded—replacing them fixed the issue. Sometimes, a dirty air filter restricting airflow or unstable fuel pump pressure can also contribute to the problem. Don’t underestimate this issue: at best, it makes driving uncomfortable; at worst, it could damage engine components. That’s why I always advise friends to prioritize checking these points and maintain the engine system regularly. If the shaking persists, take the car to a professional shop for diagnosis immediately—don’t let it worsen.

[OTravis]

When the air conditioning is on, the compressor's operation increases the engine's load, especially when in Drive (D) mode, making the engine work harder. The shaking is often caused by system imbalances. For example, if the ignition coil or distributor malfunctions, causing irregular sparks, the engine's RPM fluctuations become more noticeable. With decades of experience, I frequently encounter carbon buildup issues that cause the throttle valve to stick, preventing sufficient air intake and making the engine 'struggle to breathe.' It's best to clean the throttle body and inspect the spark plugs every 20,000 kilometers—this is more cost-effective and hassle-free than major overhauls. Additionally, worn or cracked engine mounts can transmit vibrations to the car body, making the shaking feel more pronounced. If left unaddressed, this may accelerate component wear or lead to other failures, so timely maintenance is crucial. Listen to your engine during daily driving—if you notice anything unusual, check whether the idle RPM is stable. Safety comes first.

[MacEmma]

The car shakes when turning on the AC and shifting to D gear, which is quite annoying. It's usually caused by the engine running unevenly under additional load. Common reasons include aging spark plugs failing to ignite properly or a dirty throttle body restricting airflow. When I encounter this while driving, I often wonder if it's time to replace the spark plugs, as old ones have lower efficiency and the engine output can't keep up with demand. Additionally, when the AC compressor draws power, unstable battery voltage may also cause slight shaking. If left unfixed, severe shaking can affect handling, making it difficult to control speed in traffic jams. It's recommended to do a quick check – you can inspect the air filter yourself. If the shaking persists, take it to a repair shop to adjust the idle speed or replace some parts for a quick and worry-free solution.