physically

hi OM606 multivalve in a W124.... (non turbo) i was wondering, how does the car actually switch off when you turn the key... i know its a vacuum system, but is there a specific control unit for this in the engine bay, and if so where is it? thanks Derek

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=202028&M=104%2E941&GA=722%2E328722%2E424722%2E604722%2E605722%2E629&GM=717%2E441&CT=F&cat=44V&SID=83&SGR=045&SGN=01 HELP!!, ive been told i need to replace this part (#495 on the diagram), so ive got it but where the hell is it physically located...