Try to trace the vacuum line again to see if it comes up from under the mainfold to the top area. I know it's a different animal, but that exact same hose connected to the Ignition Control Module on my 190E 2.3, goes under the intake manifold and comes back out at the rear of the manifold and connects to a Y vacuum hose that is connected to a vacuum port on top of the intake manifold.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible