What is Black Vacuum line???

[dsvw]

Hi, I have a 1986 190D.

I have a loose black vacuum line at the driver's side firewall that is not connected to anything. It is just laying there.

There is a series of vacuum lines that go through the firewall at that location for door locks that is connected to a yellow circular junction. The black line is just laying there and I think it may be the source of a vacuum leak that is causing my car to not turn off immediately.

The vacuum pump tests good and so does the shut off switch.

Anyone know where that black line should be connected?

Thanks!

[BillGrissom]

In my 1985 300D, a black vacuum tube goes from the VCV atop the injection pump thru the firewall where it is open to the cabin air. That is a purposeful leak into the VCV. The flow is restricted by the VCV and a fixed orifice to establish a vacuum pressure signal which indicated accelerator pedal position, and sent to the transmission's "vacuum modulator" (probably via a "blue saucer" in your 1986). That setup is like an electrical "voltage divider" or "potentiometer". I put a small filter in that line since didn't want any debris getting sucked in from the "clean" cabin air.

[tangofox007]

Originally Posted by dsvw

The black line is just laying there and I think it may be the source of a vacuum leak that is causing my car to not turn off immediately.

Try plugging the line and see if that solves your shut down problem. (I am betting that it won't.)

[dsvw]

Thanks.
So that black vacuum line does not go to anything? Just the open air in the cabin?

Is the black vacuum line you speak of in your car also found on the driver's side firewall, along with the vacuum lines for the doors?

I do not even see a hole where that vacuum line would go through into the cabin.

[tangofox007]

Originally Posted by dsvw

So that black vacuum line does not go to anything? Just the open air in the cabin?

That's the way it is on a W123. It's a vent for the VCV, as described by BillGrissom in post #2. The line enters the cabin through the firewall near the steering column.

[pawoSD]

Yup its like that on the W126 also, its just so the bleed air for the VCV is drawn from a reliably clean/dry source of air inside the car rather than out in the engine compartment.