During a cylinder leakage test, what does airflow out of the throttle body indicate?

Airflow out of the throttle body during a cylinder leakage test indicates intake valve leakage. This situation occurs because, in an engine, the air-fuel mixture enters the combustion chamber through the intake valves. If these valves are not sealing properly due to wear, damage, or carbon buildup, air can escape from the cylinder back through the intake system, leading to observable airflow at the throttle body. This behavior is a clear sign that the intake valves are not functioning as they should, allowing the compressed air within the cylinder to find a path of least resistance back to the intake manifold instead of staying contained for the combustion cycle.

In contrast, airflow through other components, such as the exhaust system, might point to problems with the exhaust valves, while leakage related to piston rings or cylinder walls would typically manifest differently and not result in airflow being detected at the throttle body. Understanding these relationships is crucial for diagnosing engine issues effectively.