Starting the engine
Do not let the engine run in enclosed areas – inhaling exhaust gases, which are harmful to health, may lead to loss of consciousness and even death. Exhaust gases contain poisonous carbon monoxide. It has neither color nor smell, so it is difficult to detect. Do not leave the vehicle unattended with the engine running. In this condition it is a potential source of danger.
Before leaving the vehicle with the engine running, shift the gear selector lever to Neutral (for automatic transmission – to position P) and apply the parking brake so that the vehicle does not move on its own.◄
Do not depress the accelerator pedal when starting the engine.
Do not warm up the engine at idle; drive off immediately at moderate engine speed.
If you do not intend to start the engine, do not press the brake or clutch pedal. When you press the "Start/Stop" button and the brake pedal (automatic transmission) or clutch pedal (manual transmission), the engine starts immediately.◄

Test yourself
A quick BMW X3 quiz: every answer comes with an explanation and a link to the manual page.