The engine intake valves on your VW open to allow fuel and air to enter the engine cylinders for engine combustion. They function by being held closed flush to a seat on the underside of the cylinder head with a spring pulling upward. When the cylinder needs fuel and air, a rocker arm pushes the valve open. Once the rocker arm releases the valve, the spring pulls the valve closed again so no fuel or air can escape the cylinder for compression and combustion.
Carbon build up on the intake valves can cause them to not seat properly in the cylinder head. This results in air and fuel leaking past the valve during engine compression and combustion. Worn valve springs can cause the valve to not hold closed tightly or make the valve “float” and open during combustion causing the engine to lose power.
Improperly timed engines along with broken timing belts or chains can cause the engine pistons to collide with the intake valves, bending them and causing them to stick or get stuck. Worn or broken rocker arms can also wear and bend the valve stem inside the cylinder head causing them to stick.