Intake Manifold
A manifold that distributes the air-fuel mixture (or clean air in direct-injection engines) to the cylinders.
The intake manifold (also known as an inlet manifold) is an engine component that sits on top of the engine block and distributes the air or air-fuel mixture to the individual cylinder ports. It is the gateway for air entering the combustion chambers, playing a crucial role in engine breathing, performance, and efficiency.
In port-injection and carbureted engines, the intake manifold mixed the fuel with the air before delivering it to the cylinders. In modern direct-injection gasoline and diesel engines, the intake manifold carries only clean air, and fuel is injected directly into the combustion chamber. Modern intake manifolds are often made of lightweight, durable plastic composites, whereas older ones were typically cast iron or aluminum.
Many modern engines feature a Variable Intake Manifold system (often called a runner control system), which uses vacuum-actuated or electronic butterfly valves to change the length and path of the intake runners based on engine speed. This optimizes torque at low RPM and horsepower at high RPM.
Problems with the intake manifold typically involve vacuum leaks from deteriorated gaskets, carbon buildup blocking airflow (especially in direct-injection or EGR-equipped vehicles), or failures of the runner control valves. Symptoms of an intake manifold issue include a rough idle, engine misfires, decreased fuel economy, oil consumption, or a check engine light indicating lean fuel codes like P0171 or P0174.