A cast metal or molded plastic housing bolted to the cylinder head that channels air from the throttle body into the individual intake ports. It is designed with specific runner lengths and volumes to optimize airflow dynamics and engine torque at targeted RPM ranges. A leaking manifold gasket will draw unmetered air into the engine, causing a lean running condition and a rough idle.
Spray some brake cleaner around the intake manifold while it idles to see if we've a vacuum leak.
Related terms
Throttle body
A housing containing a pivoting valve that controls the amount of air entering a fuel-injected engine.
Cylinder head
This cast metal component bolts to the top of the engine block to seal the combustion chambers.
Intake valve
A mechanical valve in the cylinder head that opens to allow air into the combustion chamber.