Why does a new car shake when idling with the AC on?
2 Answers
The reasons for a new car shaking when idling with the AC on are as follows: Carbon deposits inside the engine: When there is excessive carbon buildup inside the engine, the gasoline sprayed by the cold start injector will be largely absorbed by the carbon deposits, resulting in an excessively lean air-fuel mixture during cold starts, making cold starts more difficult. The solution is to regularly clean the fuel system, inspect the idle air control valve, and clean the throttle body. Spark plug carbon deposits: Spark plugs are wear-and-tear parts that require periodic replacement. If excessive carbon buildup or excessive spark gap is found on the spark plugs, they need to be replaced. Additionally, it's necessary to inspect the condition of the wiring, high-voltage cables, and ignition coils. An automotive computer can be used to determine the status of the ignition system. Whether the fuel supply pressure and intake pressure sensor are functioning normally should also be checked. If the fuel pump supply pressure is abnormal or the intake pressure sensor values are incorrect or malfunctioning, they can cause the car body to shake.
I just got my new car a few months ago, and one time while idling with the AC on while waiting for someone, the whole car body was shaking, which felt really unsettling. Later, I asked a mechanic I know, and he explained that when the AC starts, the compressor consumes engine power, which is like suddenly adding an extra load to the engine. At idle, the RPM is already unstable, making it more prone to fluctuations. A new car shouldn’t behave like this, but it might be due to improper factory settings or loose engine mounts with insufficient cushioning. If it’s a turbocharged car, the AC load is even greater, and the shaking might be more noticeable. I think it’s best not to ignore it—prolonged shaking can lead to engine component wear. It’s better to take it to the dealership ASAP to check the idle control system and engine mounts. They might just need to do a software update or tighten some screws to fix it. After all, since it’s still under warranty, don’t waste the opportunity.
