Bit of an old post but since almost nobody has commented yet...
It's been raced moderately hard, and by the sounds of it probably has no had the easiest life. If it's done more AutoX and track days than it has spent time cruising on the highway, it's incredibly likely that the engine is just... done.
I'm with Eggman, sounds like it's losing compression, misfiring, or a host of other possible options, all of which your dealer should have codes set for to make the diagnosis go a lot quicker. Here in Canada the engine has a 10 year 160,000km warranty, I assume it's not the same for you?
View my fuel log 2018 Mirage ES 1.2 manual: 43.5 mpg (US) ... 18.5 km/L ... 5.4 L/100 km ... 52.2 mpg (Imp)