Hey all ! 1985 w123 300 tdt wagon federal
So car shuts down after about 20 seconds of turning
The key off.
So far isolated ignition vacuum system
Disconnected locking system

Tested the system ignition line
Shut off line and shut off valve are air tight


The brown hose to ignition gets
Around 22 in of vac.
When i vac directly to
Shut off valve the car shuts off around 8 "of vac
I noticed the shut off line receives vac pressure
Very slowly . Why is that ? Is that the culprit? Is there
Something in the ignition that governs how much. Vacuum to send
To shutoff?
Thanks !

Yes. At about 1-2 O-clock on the Steering Colum Lock there is a Vacuum Switch. When you turn the Key a Cam inside of the Steering Colum Lock actuates the Valve.
That particular Vacuum Valve is about $30 each plus shipping.
Before you remove that Valve note which Tubing is connected to what nipple. One of the Tubings is brown with a stripe and the other is just Brown.
Swapping the Tubing to the wrong positions also produces the symptoms you are having.
Mercedes Part number 0004600284 shutoff valve on steering Colum.

However, before ordering check to see if the little Rubber Sleeves are OK where they connect to the Valve. Perhaps one of the Sleeves is bent/pinched and restricting the Vacuum Flow (if there is such a thing as vacuum flow).

Also look under the Hood for the other Brown Vacuum Tubing that eventually connects to the Main Line and make sure the Rubber Connectors are also not pinched/bent causing a restriction.

Good job trouble shooting.

If you are also having Ignition Switch or Steering Colum Lock problems the Steering Colum Lock normally comes as an assembly with Vacuum Valve. Ignition Switch and of course the Steering Colum Lock itself.
I bought one of the Steering Colum Lock assemblies from the Mercedes Dealer and it was made in France by Neiman.
There is aftermarket Neiman/Valeo Steering Colum Lock assemblies for slighly less.
Be, careful as Myele sells the bare Steering Colum Lock.

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84 300D, 82 Volvo 244Gl Diesel

I fogot to mention someone over on the Ozbenz Forum found the steering coulum shutoff valve itself partially plugged. So maybe try spraying it out with something line WD-40.

I would not use Brake Cleaner for that as Brake Cleaner softens some Plastics and part of the Valve is inside is plastic.

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84 300D, 82 Volvo 244Gl Diesel