I drive a Nissan Qashqai 1.2 Turbo. Is it necessary to let the engine idle for several minutes before switching the ignition off?
Turbocharged engines do need to cool down before they are turned off. But in nearly all driving conditions, the engine does not reach temperatures that require a deliberate cooling down period.
However, if you take your Qashqai to a race track and drive hard for two or three laps, then you should give it another lap at a moderate pace and a period of idling to restore normal engine oil temperature.
Switching off when the engine is very hot stops the circulation of oil. The layer of oil around the turbocharger bearings stop flowing and literally gets "burnt". The black sludge that forms is similar to what you find on a burnt frying pan. That is not good for any engine.
In all other situations, even sustained high-speed driving on Malaysian highways, there is inevitably a period of low-speed driving before parking the car or switching off the engine. That is sufficient for the engine oil to cool to a level that will not damage the turbocharger bearings.
Also, always ensure that you are using the recommended grade and viscosity of engine oil for your car.