Bro there are a million different opinions on this issue.some people say u dont need to idle a car for more then 30sec before driving in the morning, others say do not drive until the engine reaches operation temperature.
What i do is that i start the car on petrol, in the morning when the engine is cold.let it idle for around a minute (rpm stays above 1500) and then i start driving it but very slowly, no revving past 2500rpms.with in a km,the blue (cold engine) light goes away n then i switch to cng. i dont know if thats fine or not but thats doing okay for me n i recommend it to others too.
As for RPM reaching near 2000 in the morning is normal for almost all new cars these days.engine warms itself that way so that u dont have to.it slowly falls down to normal level i.e 800rom. it shudnt drop below that, if it does, theres some problem in ur car as u say it goes down to 0.
and im not really sure if there is blue light in new city or not,i think there should be one but im not sure.will have to confirm that.dont u see any blue light even when u turn on the ignition before starting the engine?