Many modern engines incorporate swirl flaps into their intake manifolds. These allow for the electronic control of airflow. By controlling the airflow with the flaps there is a greater ability to regulate the fuel-to-air ratio. This aids in emissions and improves low-end torque.
Over time these swirl flaps which are just a butterfly valve can accumulate carbon and oil from the breather system. This can cause them to stick. On the Mercedes with the OM642 engine, the movement of the flaps is controlled by the swirl flap motor. The motor has a plastic arm that is attached to the plastic arms on the outside of the intake manifolds. Due to the constant heating and cooling cycles in the engine bay, the plastic will become brittle over time. The brittle plastic combined with the sticky flaps can cause these arms, often called swirl rods to snap. A failure with the swirl flaps will cause low power, limp mode, or a CEL. The most common codes are P2006 and P2007. You may be able to verify this issue by visually inspecting the rods or trying to move them with your hands.
Mercedes does not offer the swirl rod as a replacement item. Previously, the only fix was to replace the entire manifold. Depending on the model these manifolds range from $300-$800 each. There are now upgraded metal swirl rods that can be used to replace the old plastic version. The first step should be to clean the intake manifold to be sure the flaps are moving freely. The metal rods are a direct replacement for the plastic ones. They hold up much better because they do not degrade like the plastic ones do. The linkage that attaches the swirl motor to the rods and the swirl motor itself are available separately.
Previously a failure of the plastic swirl rods would mean replacing both intake manifolds. For an NCV3 Sprinter, this would be over $1200. Using the replacement components and only replacing the parts that are broken would be under $400.
If you are removing the manifolds for other repairs, such as the oil cooler seal replacement, it would be a good time to inspect the manifolds. Make sure the butterfly valves are operating smoothly. This would be a good opportunity to install the metal swirl rods as a form of preventative maintenance.
