What Causes Vehicle Shaking When Idling with AC On?

[JoelFitz]

Here are the reasons for engine shaking when idling with AC on: 1. AC not increasing idle speed: Normally, a car's idle speed is maintained around 800 rpm. When AC is turned on, the idle speed should correspondingly increase to generally over 1000 rpm to prevent shaking. 2. Faulty ignition coil or spark plug: If the vehicle experiences slight hesitation during acceleration or minor idle instability without AC, but shows obvious idle shaking with AC on, it indicates issues with ignition coil, spark plug, or cylinder wires, suggesting incomplete combustion or cylinder misfire. 3. Excessive compressor pressure: Overly high AC pressure increases engine load and causes shaking. Common causes include poor condenser heat dissipation, excessive refrigerant, or dirty AC lines leading to high pressure, which may indirectly cause vibration.