Vacuum line cap?

[rich4316]

I recently replaced the fuel line from the CSV to the fuel rail.  When I moved the car,I located a vacuum line cap under the car.  (During the work, I did not remove any vacuum line caps).   It’s black and had just a little oil residue in it.  I have no idea where it is supposed to go.  I’ve looked on the realoem diagrams, but couldn’t find it.
Thanks for any assistance.  

1988 535is


 

[Mike W.]

I don't remember the routing, but a first WAG would be it's for then interior temp sensor, down by your knee.

[Blue Shadow]

Check the bottom of the intake manifold there are connections there and all should be plugged, one with the suction line to the interior temp sensor Mike mentioned.  

[rich4316]

Thanks for the assistance!  It would make sense it was from under the intake since I had my arm under it while getting the fuel line in.

 

[DavidE9]

Maybe this will help:
https://www.youtube.com/watch?v=BYxeCXNJP2Q