No sputtering just before stalling seems to be a "hard" failure . That indeed seems to point to an electrical problem.You indicated that after a brief pause (call it : cooling period) you are able to start your car again. This tells me you have a thermal contact failure , most likely a bad/oxidized connection or wire with a high electrical resistance.When under power after startup it heats up , expands and interrupts the circuit . After cooling down it contracts and "reconnects" again.
Since you checked all ground connections and replaced the coil and dizzycap I regard them OK
You might try this:
1 .Temporarily "hot wire" your ignition coil
direct to the battery . This rules out any bad electrical wiringcontacts / connections in the car's wiringcircuit between battery and coil.
a. If your problem persists , your wiringcircuit up to the coil seems to be OK. Go to step 2
b, If it solved your problem check wiring and connections at/between battery, alternator,ignition switch and lightswitch . Lightswitch ? Yes ! Its terminal 30 acts as a kind of terminal block between alternator/battery and ignition switch.Check for a bad or oxidized connection.
2.connect a stroboscopic timing light to one of the sparkplug leads.After your engine stalls again ,try to restart it immediatly and observe if you have a spark ( your timinglight should flash)
a.No spark means an electrical problem in either the HT wire from coil to dizzy or the 123 dizzy(connections) itself . Since you did not mention replacing the rotor finger, you might replace that one as well. It has an internal resistor that does sometimes fail and results in erratic behavior . If still no success, reinstall your old mechanical dizzy and see if that solves your problem. If so, your 123 dizzy has most likely an internal failure.
b. A good spark should indicate a correct working ignition and electical wiring circuit. Your problem lies somewhere else.
You may have a look at my mini tour about 230SL bad engine starting /running
It starts here :
https://www.sl113.org/forums/index.php?topic=38391.0Good luck !
