Considering the job of the shutoff mechanism is to cut fuel, yes, a faulty shutoff mechanism can restrict fuel in/to the IP.

Yes, preglow is only to get the engine started and from '90 to help the engine stabilize for a minute or so when it's very cold (afterglow is MB's term for this feature). I used glow as a reference because turning the key to the glow position vents the line that routes vacuum, as it were, to the shutoff actuator. If the vent port is clogged or the key switch malfunctions, the shutoff actuator isn't fully released and thus confounds proper fueling of the engine.

If it's not obvious, I'm grasping at straws If a turbocharged car is slow, you blame the turbo. If a naturally aspirated car is slow, you blame... what, the owner?

Sixto
87 300D