You need to check and see if you have electronic control of the fuel injection system (CIS-E)

If you do not, the car will run in FOM (fixed operating mode)- no assitance (enrichment) for cold start.

If I recall, with the key in the position just before engaging the starter (KOEO), you should read 70% at x11/3 diagnostic port with your multi-meter if engine recognizes the "E" potion of the CIS-E system. While running, your duty cycle may be 'stuck' at 50% (FOM). There are other codes as well, that are represented by 10%, 20%, 30% etc readings.

do some searches on the subject for some expert posts.

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E