2006 Nissan Van High Idling

The car is 2006 Nissan AD van which I bought 2 days ago. The idling is abnormally high and the vehicle is accelerating to 70 Km/hr without stepping on the accelerator. When I took to a mechanic he told me to buy carb cleaner but even after spraying the cleaner on the airway there was no change. In fact it started accelerating periodically.
I noticed the idling was coming back to normal when he disconnected the sockets going to the air cleaner or the accelerator