I wish I could offer some good advice. Just
to clarify the proportioning valve is the white
plastic apparatus afixed to the injection pump,
and its purpose is to bleed off vacuum as
throttle position changes. I changed mine
to make sure this was not the problem.
I remember reading that 5.5 to 6.5 Hg was
preferable when the lever was 10mm from
the stop pin. At full throttle the lever should
nearly touch (.5 mm away) the stop pin. At
this point I think vacuum is supposed to be
completely bled off, but when I applied vacuum
it seemed to be slow to release. I can't help
but wonder if that charactaristic is normal.
I had more websites than I could handle when
doing a websearch on the subject. I take pride
in my 82' 300Sd and it will be the last automatic
Mercedes I buy (unless getting a steal) because
I do not have the brains to troubleshoot modulator/
vacuum parameters. Good luck, sorry in advance
if I have only stated the obvious.