I recently went through all the under-hood vacuum connections on my 1985 w123 300d 146k miles. I'm also in the process of removing all the emission components off this car and therefore I have removed the vacuum circuits for them. Somehow the first time I did this, I got a few connections backwards. Despite this, all of my up shifts were firm and on cue but downshifts were clunky, loud, and harsh. None of my shift's max speeds ever went over 4400rpm. Now that the vacuum system is wired correctly, the downshift clunks are nearly silent but now flares on all up-shifts WOT or not. Before shifting, the engine now revs out to 5100 on first, and then to 5300 on second... atleast according to my tach. All gears accelerate to a certain rpm and hold there for 1-2 seconds before they shift. What could be wrong? I have adjusted the bowden cable with no effect multiple turns either direction. The bowden cable is still under spring-load so I know it's not broken. And I have applied vacuum to the modulator and it held vacuum....

There is a procedure for adjusting the vcv
Also, there are set measurements for the throttle linkages.
Try these two parameters and report back

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1983 300CD Turbodiesel

There is also a calibration for the modulator
Didn’t read anything regarding the adjustment In your post

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1983 300CD Turbodiesel

What you describe is what my car did when the kickdown switch behind the accelerator pedal got stuck down. They get sticky with age. Try unplugging that first and see if it goes back to normal.

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1984 300D Turbo 200K

What are you driving Fang? If it is a W123 with an OM617 engine, your problem is almost certainly a failed vacuum connection. The hard vacuum lines are also pretty brittle at that age and easily cracked or broken while manipulating.

Look for the simple things first. The fact that your problems started after messing about with the vac tubes and connectors is a clue.

I also do not recommend adjusting the vcv and linkages unless you have adjusted them before. They are factory-set and should never go out of adjustment. My 36yo example has never been touched. Solve your vacuum problem first.

Did you plug the pipe ends after they were removed, if not ...

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David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)