This study focus on the effect of engine specification, driving conditions and the vehicle type on the idle emission characteristics. In order to obtain the characteristics of exhaust emissions, 1,260 vehicles of spark ignition engine are sampled and investigated. The exhaust emissions are measured with a CO/HC emission gas analyzer. The Sl engine vehicles are investigated by the effect of various exhaust emission parameters such as vehicle milage, engine specification, valve trains and fuels. The results show that the amount of CO and HC emission is not directly related to the driving mileage of the vehicle. However, the engine specifications and fuels such as the type of valve train and piston displacement have influence on the exhaust emissions. In addition, the LPG vehicle emits more CO and HC than gasoline vehicle. Based on the test results of SI vehicles, the influence of excess air and displacement volume are discussed.