Mercedes Benz repair: diesel wont shut off, vacuum pump, vacuum system

Question
I recently purchased a 1982 diesel 100 sedan to convert to burn vegetable oil.  
The problem I have is that the engine keeps running after the ignition is
switched off.  To shut the car down, I have to open the hood and press the
throttle down manually.  Any ideas on how to fix it?  Thanks.

Answer
Answer:
All the data you need is in the following links.

Run away diesel, why does it happen?
http://www.mercedesshop.com/shopforum/showthread.php?t=101404

Motor / engine keeps running
http://www.mercedesshop.com/shopforum/showthread.php?p=80108

How to Replace Your Shutoff Valve
http://dieselgiant.com/repairyourshutoffvalve.htm

Rebuilding the Vacuum Pump on the 617 Engine
http://207.210.95.34/~boostd/easley/Rebuild_vac_pump.htm

1982-240D-Vacuum System
http://www.mercedesshop.com/shopforum/showthread.php?t=105201

Vacuum pump lesson learned
http://www.mercedesshop.com/shopforum/showthread.php?p=872760

Vacuum Pump Gasket Sealer & Torque
http://www.mercedesshop.com/shopforum/showthread.php?t=138153