Make it absolutely certain that you have a very thorough idea of what to do when replacing the shut off valve. Larry Bible, one of the long term members and an excelent tech here blew his rebuilt 300D last year after replacing the shut off valve. The little hook on the end of the vacuum shut off assembly does not get where it should and will force the IP to work as if wide open.
The problem is that if not installed correctly, after your start the engine it will build up revs until the turbo kicks in and then run away until it blows up.
The way it was explained to me, and has worked so far, is to carefully remove the old one and note the position you need to turn it to unhook the lever from the inside of the fuel injector.
It just pulls out and then needs to be twisted slightly to get it loose.
Then carefully put the new one on there, and get it to hook inside. Pull the shut off away slowly while hooked and you should feel the slight springiness of the internal part resisting your pull. With that it should be safe to bolt it in and start the engine.
But keep wrenches at the ready to loosen injector lines if it starts to run away from you. Nothing else will stop the engine until it is left in pieces on the garage floor.