preparation is going good bro.its the easiest paper among the three, so wont be an issue
well well well, 17km/ltr is gud enough bro! im surprised to hear that rpm problem of urs! before i start to guess the problem , let me say " tuning kara lo paa ji" hehehe... ur car needs it badly.
as for the check engine light, today, when u go to the garage to say good bye to ur car (since u have this ability of talking to ur cars, are u micheal knight? :P) open the hood, take a spanner out and unhook the battery terminals of ur car.let them stay off for 30mins or so.whole night wud be fine too.this way, u r gonna reset ur ECU the manual way.
similar thing happened to me once, the car would start and then as soon as it switched to cng, the rpm wud drop down to ZERO! even if it was at 6000 when on petrol. fortunately, the doctor of my car was nearby, i called him and there he came with his diagnostic tool.he plugged it, reset the ECU and off it went!! problem solved!