Big thanks to this forum especially to inputs of Stevebfl.

My 1992 E300 24 valve cisE suffers from severe warm hesitation with black smoke since I acquired it 2 months ago.
and last week goes into limp mode with max speed of 20 kph
and carbon build-up on plugs probably because of wiring harness
issue.

Coz of difficulty of sourcing and cost, i have it rewired for $100 by an electrician as temporary measure.
so far it has been doing well against the advise of an MB enthusiast coz it might affect performance as experienced by some.

But anyway despite rewiring i still have warm hesitation, black smoke, 0-100 in 20-30 sec, stalling even if i unplugged the coolant temp sensor, R16/2 resistor and using 95 octane gas.

After reading the forum last night, this morning i tried to adjust the AF (CO) because stalling and backfiring indicates lean mixture. after several rotation stalling resolved, i test drove it and runs fine. I planned to unplug Ox sensor but dont want to dirty
my hands

but after lunch with warm weather stalling returns.

FINALLY, I TRIED UNPLUGGING THE EHA (the final step in ECU control of fuel metering), the stalling resolved and runs better
and smoother.

NEXT DIAGNOSTIC PLAN is to unplug Oxs, replug the EHA
and unplug or replace sensors
that are telling the EHA to run lean
1. CTS
2. altitude sensor
3. air temp sensor (none)

Hope to find the culprit sensor and that the ECU is not the problem and return ECU control mode for better emissions.

Without EHA, car runs like a carburated engine without computer
control and probably can be suggested as an emergency
measure but make sure that the AF mixture is first adjusted with EHA removed because it mighty be on the lean side and the engine will stall.