Using fuel gas for gasoline engine can be made with additional equipment which is called Conversion Kit. However is still limited because there is a problem about the engine performance, that is too high idle rotation and low acceleration if compared to engine with gasoline. One at the cause of too high idle rotation is too a little fuel gas enter to intake manifold and specific gravity fuel gas (0,562 kg/m3) lower than gasoline, that cause the idle condition where the intake gas valve opened just a little, air that enter together with fuel gas cannot doing completely combustion. The way to improve this problem are by supply fuel gas with injection system control by electronic in idle and aceleration condition