Turbo Actuator (2002-2003 ONLY)

Also known as the "Pressure Converter Valve"
 
This is a vacuum actuated turbo boost controller ONLY for the North Americal Model OM612 turbo diesel 5 cyinder engines found in ALL 2002-2003 Sprinters. 
It commonly goes bad but it's malfunction does not turn on the Check Engine Light. However, the engine will feel low on power and the turbo will not be functioning. 
A sign that it is going bad can be a surging of turbo boost while driving on the highway.