Twinion

Hello there i have recently bought a C200 CGI 2014 and the car runs smooth and great and all and i have changed the oil , gearbox oil , break fluid and the coolant also cleaned the injectors with some device in the workshop and also changed all the spark plugs , the problem is whenever i drive the car for an hour or so and when the engine is fully warmed up when i put the gear on P or N the rpm starts Fluctuation between 700 and 800 rpm , whenever i press the gas pedal or change to D or R gear it stops and it surges every 5 seconds from 700 RPM to 800 RPM and goes back to 700 rpm the mechanic i talked to said that its common problem with all c200 CGI engines and i can't do much about it its driving me crazy , also the place i live we have no premium fuel available so i have to use regular fuel and use octane booster please help me out heres the video of the situation