You need to do a transmission shift cable adjustment .If the cable is set to tight [no play] it will want to drive off .Or the small micro switch in there for the throttle quadrant is broken inside. And the computer thinks its still on drive settings .Look inside the hood to the place the linkage goes to the fuel flap ,look for a switch see if it clicks on and off as you open the throttle . I will find a picture if i can

I'm confused:

'84 SD with '83 engine and '82 transmission = what computer?

Control pressure cable tension doesn't affect TC stall so it can't affect how much the car creeps in D while idling. Neither does modulator vacuum. The transmission doesn't know the brakes are applied.

Maybe the tachometer is reading low. Way low.

Sixto
83 300SD for sale
98 E320 wagon

I changed the 84 tach to an 83, because there was a changeover at that time. I also installed the proper tach amp under the hood.

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1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI