A broken intake valve typically causes what issue?

A broken intake valve can cause air to flow out of the intake air filter rather than into the engine as intended. In a properly functioning engine, the intake valves open to allow the air-fuel mixture into the combustion chamber, where it is compressed and ignited. If the intake valve is broken, it can no longer seal properly, which may result in air escaping from the intake system instead of being drawn into the engine. This malfunction disrupts the normal air intake process critical for engine operation.

In contrast, the other options present different issues that may not directly relate to a malfunctioning intake valve. For example, fuel leaks would typically be associated with fuel line or injector issues, and excessive emissions could stem from incomplete combustion or issues in the fuel delivery and ignition systems. Cooling system failure is generally tied to problems with components like the radiator, water pump, or hoses, rather than the intake valve. Thus, the air escaping from the intake air filter directly correlates to the consequences of a broken intake valve, highlighting the correctness of that response.