Looks like it could be the control plunger that is connected to the air intake flap arm and distributes the fuel to the injector hoses. It probably runs through "O" rings which may have become sticky since the car has been idle. It may mean taking off the top plate on the distribution block to free it off so you may need a seal kit, if you can still get them.

Try having a look at this http://www.benzworld.org/forums/w116...eshooting.html it may be of some use to you.

Steve