why advancer was not installed in the first place? it is a very essential component. maybe u didnt get ur car converted from a good place..just my opinion.
theres no solution to the vibration. get ur kit tweaked from al-mubarak cng or some good place. tell them to increase idling rpm. but even then a little vibration will persist. all engines vibrate more on cng. my vti vibrates more than usually when its air filter is not clean. so change urs when its dirty...when u cannot see light passing thru it.
do not drive ur car on high rpms on cng. its bad for the engine. my vti also gives off a lot of sound when i rev it to high rpms.
change ur attitude while u drive on cng... when u drive on cng u r driving in econo mode (a feature thats dere in ur car.) do not accelerate hard. do not drive on cng when going uphill. thank god that u r gettting a good economy as compared to petrol...cuz ride doesnt remain the same on any car on cng as it is on petrol.