300d ...i have a non functional cruise unit...the accel works on the stick but nothing else.....today whilst poking about under the hood, i noticed that there is a black plastic pipe coming out of the front of the unit with a gray plastic nut holding it on.....i followed the pipe back to near the battery, where it just stops....i checked the other side of the firewall, but there doesnt appear to be a corresponding pipe....does anyone know where this is supposed to go?...is it a vacuum line?...i am a bit baffled

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88 709d moved on
82 406 moved on
82 240d moved on
81 230e deceased
79 240d deceased
73 230.4 moved on
96 210 300 td moved on
92 201 moved on
82 280e daily driver
79 300d keeper
81 240d deceased
87 hymer 660s (408) keeper
......................... You can NEVER have too many cars

But as I remember on my 1980 the cruise control had the old vacuum type which has a cabe coming out the front that connected to the throttle linkage on the side/top of the valve cover.
The odd thing is that if you can accelerate then it is connected to something. The vacuum connection was on the back or side I think?

The cable sleeve was held in place by the plastic nut you are refering to. Could it be that someone has put an aftermarket cruise on the car?

Sorry wish I could be of more help. Can you shoot a low res picture of it?

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

On those there should be the cable to the linkage assembly on the valve cover and the black (yellow stripe?) vacuum line that ties in to the vacuum splitters at the firewall.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

these are pics of the cruise unit and on the second image the end of the pipe (the one with the gray nut on the unit, the black and yellow vacuum pipe appears to be connected ok

Attached Thumbnails

   

__________________
-------------------------------------------------------
88 709d moved on
82 406 moved on
82 240d moved on
81 230e deceased
79 240d deceased
73 230.4 moved on
96 210 300 td moved on
92 201 moved on
82 280e daily driver
79 300d keeper
81 240d deceased
87 hymer 660s (408) keeper
......................... You can NEVER have too many cars

maybe its just a vent tube when cruise is turned off

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350