Sounds like the Mitsubishi GDI engine if I am not mistaken. Do you do a lot of short journeys? Give the car a blast along the Motorway at high revs to clear the build up in the engine, some refer to it as an 'Italian tune-up'. A lot has been discussed about the GDI engine, if you do a search you will find piles of info. Oh, and welcome to the forum. Please excuse my manners.