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My used Caddy 1.9 TDI has a problem with the turbo.
It has a boost gauge which was not working until I fixed it.
When the turbo is plugged into N75 solenoid, the boost gauge would not go pass 20 kpa.
It's like it's consistently having a small boost.

I cleaned the MAF, swap out solenoids but it didn't seemed to solve the problem.

Accidentally, however the mechanic plug the turbo vacuum line into the EGR solenoid.
The boost gauge came to life, hitting 150 kpa.

At first, it didn't seemed to run right though. Only at light load, 3rd/4th gear; and small acceleration did the boost gauge showed max of 150 kpa. Then it would died down.

Today, I tried to spray some lubricant onto the actuator, hoping to free any stuck actuator and redo some vacuum lines.
By intentionally plugging the turbo "wrongly" into the EGR solenoid, it appears to run pretty well.
The boost is going up when I rev the engine and coming down when I let go the accelerator pedal.

I feel like keeping this configuration, as I see nothing wrong with the engine running.
Temp gauge is normal, doesn't appear to have any overheating.

This van is a mess. It had 4 previous owners. Since it's a commercial vehicle, the workers probably trashed it or someone did something and messed around with the wirings etc. The EGR vacuum was not even connected when I got it. There's no CEL light but some codes which I vaguely remember...something about boost not equal.

Maybe the EGR wiring is not even the original EGR wiring, but really the Turbo, for which I have no idea.

But I'm curious if there's any side or bad effects, assuming that's the real EGR signal.
 

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Look through the low power FAQ article. There's a vacuum diagram for the ALH engine. It should be similar but at least give you an idea of how it should look.

You can swap the N75 and EGR solenoid as a test. Change the plugs, everything. If that fixes your problem, you have determined that the N75 solenoid or its wiring, or vacuum line are bad. Inspect the wires and vacuum line all the way down to the turbo.
 
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