Why does my Audi A2's engine rev while idling?

Recently I've noticed that my Audi A2's engine is idling at a higher RPM than usual. This happens even when the car is stationary and causes the car to vibrate. What could be causing this and how can I fix it?

It is possible that your car's idle control valve needs to be cleaned or replaced. This valve helps control the engine's idle speed and can become dirty or malfunction over time. You can try cleaning it first or taking it to a mechanic for a replacement.

Another possible cause could be a vacuum leak. This is when air enters the engine through places it shouldn't, causing it to run rough or rev while idling. A mechanic can use a smoke test to check for any leaks and repair them.