It is the air temp sensor for your cabin, climate control uses it to monitor the inside temp of the car. I do not believe it has any vaccum line connected to it, my 420 also do not have a vac. line to it.
I hope this helps.
Thanks

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)