Hi,
I appreciate some help about my '87 300D,

There is an electronic diesel control (EDS) in this car that regulates the idle speed and other things, it also provide the signal for the tachometer. I am not sure if it works OK in my car, also this is a possible cause for intermitent AC compressor cut off.
There is a test connestion in front of the battery to the left, it has 4 poles. You need to open the plastic door or so and pull the connection from the buttom. terminal # 2 has 2 gr/yl wires in it.
Terminal #2 is the engine speed signal comming from the EDS, the test in the CD says that:
AC~ voltage measured between terminal 2 (as +) and a negative source (car body) should be "" > 4 V AC with rising speed, rising voltage ( < 3 V AC with ELR)""

I measured mine and it was about 11.7 V AC, if I measure using DC voltage it is about 5.5 V DC..
There could be mistakes in the CD and a confusion between gas and diesel, also I heared there is different versions of this system... and I am not sure that I understand what they said in the CD as in the previous qoute. ELR is the idle solonoid or so, does this mean it should be about 3 V AC at idle without EDS!!...

I am confused and I appreciate if one owener of similar car could check this for me at his car, without AC on. And if somebody knows more technical explanation.

Thanks,

ALso, there are 3 other wires on this test terminal, does anybody know what they are for and how to check them...

Are you having a problem with engine performance? If not, than I recommend shifting the attention to another area. What problem needs to be addressed?

There is a crankshaft sensor which I believe is responsible for generating the RPM signal. At the moment I am unable to recall if this is hard wired to the EDS control unit connector or if it has a separation point. I can look later to see.

For grins you may want to remove all your fuses (one at a time) and polish the tips. Before reinstalling fuses push the spring loaded tab downward, this will increase the tension to the fuse once it is reinstalled.

Not a lot of time invested with this approach, good starting point.