Your Turbocharger has a "Pressure Air Dump" valve nicknamed a "Wastegate"
[It "Dumps" the Exhaust (Powering the Compressor Wheel ,on the other side
of the Turbo Shaft) back into the Exhaust System,thereby DePowering the
Turbocharger.]

The "Wastegate" on your Mercedes 124.128 Chassis (602.962 engine) is
operated by an Electro/Vacuum Signal from the EDS (Electronic Diesel System)
[AKA the Computer]

Disclaimer:
I'm crazy if I tell you you haven't altered your Turbocharger Wastegate...
Because ALL the Damned Electro/Vacuum Actuators that control the
EGR/Emissions system are ALL in that area you described.
AND I REALLY don't know which one you've been playing with.

(I kinda Glommed onto the idea that the Actuator you had aholt of was for
the EGR...because it had [from your description] a Vacuum line connected to the EGR...BUT Who
Knows?)

The whole point of the Pressure Operated Wastegate Saga I've been steering
you towards...IS...It Simplifies the wastegate system AND removes it
from the Computer's control.

I.E.

Boost goes up to 14 PSI ...Wastegate opens...Period.

__________________
'84 300SD sold
124.128