yes sir, it's quite frustrating when your 4 cylinder engine feels like an old 3 cylinder carby engine due to the vibrations : (
so, the mechanic did throttle service, spark plugs checked (they were okay), he also tried by replacing the coils with other ones available in the market but the engine behaved same on replaced coils ..
the car has no CNG ever ..
he then adjusted tappets (according to him), but the issue is still there..
so .. now he suggests it has some valves problem .. the engine would need to be opened ... and there might be issues in it.. so keep 35-50 thousands in your hand before going for that job : (