During the warming-up period, the amount of hydrocarbon emisson is very high. In order to reduce hydrocarbon emission in gasoline engine, it is necessary to estimate the fuel and fuel product flowrate in the emission gas. The fuel in the intake manifold and cylinder is estimated by the "wall-wetting" effect calculation. The rapid prototype engine controller has been developed by using MATLAB, SIMULlNK, REAL TIME WORKSHOP, and WATCOM C++. The sensor data from the engine is transferred to laptop computer, and the fuel delivery is calculated. The fuel is injected into the engine as the engine controller of the laptop computer calculates. The fuel control logic in the cold start condition is based upon the "wall wetting" effect calculation. By combining the technologies described above, development of a controller to reduce the hydrocarbon emission during cold start is the focus of this study.