Do you get 12V across the pins at the switchover valve connector when you turn the key to run/glow and while the engine’s running? Put your finger on the switchover valve and have someone turn the key to run/glow. Do you feel a click? Seems like there isn’t a signal or the switchover valve isn’t responding if vacuum remains available to port 3 during cranking.

For kicks, swap the shutoff switchover valve with the EGR switchover valve. That can cause an EGR fault that makes the ECU cut boost but you only need to test while idling.

If you still have that ‘87 TD, swap instead with the overboost switchover valve between the manifold and the ALDA. Don’t worry about the hose to port 2 if that valve doesn’t have a port 2.

Sixto
98 E320s sedan and wagon
02 C320 wagon