Why at full temp the engine runs great when not at full temp it sputters then stalls?

When an engine is not at full temperature, fuel and air may not be mixing properly due to increased density and viscosity, leading to incomplete combustion. Additionally, components like the fuel injectors and spark plugs may not function optimally until they reach their ideal operating temperature, causing sputtering and stalling. Cold engine conditions can also affect the fuel vaporization process, resulting in poor performance until the engine warms up. Once at full temperature, these systems operate efficiently, allowing for smooth running.