Intake Runner
Individual tube passages of the intake manifold that guide air from the central plenum to each cylinder's intake port.
An intake runner is an individual tube or channel of the intake manifold that connects the central air chamber (plenum) to each cylinder's intake port on the cylinder head. The runners carry the filtered intake air (and fuel in port-injected engines) into the cylinders for combustion.
The length and diameter of the runners are carefully tuned to optimize engine performance. Longer, narrower runners improve air velocity at lower engine speeds, enhancing low-end torque. Shorter, wider runners allow for maximum airflow at high engine speeds, improving high-RPM horsepower. Many modern vehicles use variable intake manifolds equipped with runner control valves (IMRC) that adjust the runner length electronically based on engine speed.
If the gaskets sealing the runners to the cylinder head leak, unmetered air will enter the cylinders, causing a vacuum leak. This leads to a lean air-fuel ratio, rough idling, and engine codes. Diagnostics involve spraying soapy water or using a smoke machine to check for leaks around the manifold base.