please clarify ...
-- if u set petrol rpm at 900 then ur car doean't give u any problem may it be early morning start where auto choke kicks in and advances rpm for a while till engine gets adequately warm
if above is true it is your cng kit issue .. there are internal settings of springs in cng kit plus the one who tunes it has to ensure that it has no air leaks .. either of the two issues
if the problem of cold starting is with petrol as well then it is your auto-choke sensor or the motor which synchronizes with it to advance acceleration ....
but i'm quite confident the main issue is the cng kit ... there is an idle advancer in cng kit .. how come it is not working .. it gives some gain in rpm .. if u experiment with air-chocking while car is on cng even that increases some rpm ... so i don't understand what is the exact nature of ur problem
u can check the function of auto choke by turning on ac .. if it inc rpm with ac ur auto-choke is perfectly fine
then there is a reset option also .. have u tried that ... remove battery leads for about 30 sec .. and put them back