I have one Mercedes Benz vacuum cross over valve for W123 and W126 turbo diesel cars. I bought this to troubleshoot one of my cars and it was on the car for less than half an hour. I have to say its used.
This solenoid is energized and allows vacuum on the alda valve on the injection pump to richen the fuel mixture under turbo boost conditions. When it doesn't work you won't get the extra power from the turbo. Its also used on other Mercedes cars on various applications
This crossover valve is made in Germany by Trucktec. The part number 001 540 86 97. Its also the Mercedes part number. Free shipping in the USA.