Is It Normal for the Car to Shake When Idling with AC On?
2 Answers
It is normal for the car to shake when idling with the AC on. During idling, the engine runs at a low RPM with limited torque, making it feel underpowered when driving the AC. The engine powers the compressor of the car's air conditioning system to produce cooling. The compressor is a significant load on the engine, so when the AC is turned on, the engine has to work harder to drive the compressor, resulting in noticeable shaking. If the throttle body is dirty, it can affect the engine's performance, and turning on the AC at this time can worsen the idle condition, causing the steering wheel to shake. Cleaning the throttle body can help prevent this issue. If the idle RPM increases, it indicates the compressor is active; when it's not working, the idle RPM drops, and the steering wheel won't shake.
My old car occasionally has slight vibrations when idling with the AC on, which I think is quite common for vehicles with over 100,000 kilometers. When the AC is turned on, the compressor kicks in, suddenly increasing the engine load, which can cause unstable idling. Another car I drove before had the same issue, and after inspection, it turned out to be a problem with the ignition system—aging spark plugs causing uneven ignition. After replacing them, the vibrations reduced significantly. Minor fluctuations are normal and nothing to worry about; but if the shaking is severe or accompanied by unusual noises, it’s time to be cautious—it could be due to a dirty throttle body or loose engine mounts. I recommend paying more attention to the air filter and ignition components during regular maintenance, and periodic cleaning of the throttle body can prevent bigger issues. When the engine is healthy, the vibrations will be much less noticeable, as the idle state itself is quite sensitive, and any additional load can easily be amplified.
