How do I fix my RC car that goes forward by its self?

When a Car starts to move forward on its own, as soon as you turn on the car, then you need to check the following

1. Check your trim on the transmitter is not turned up or need adjusting
2. If an electric car then you may need to calibrate your ESC
3. If a Nitro Car , then check your carb is not taking in too much fuel

These are the quick fixes, and are normally the cause of the moment