Hello to all, 1984 380SE, recently the car stalls once in a while, and gets more frequent. From once few days to once few minutes, and now the car cranks, but will not start.

I have replaced the following:

Fuel pump, fuel filter, fuel accumulator and ignition coil. Ignition/spark plug wires checked ok (~1.1k ohms), and all spark plugs checked out normal. The car still cranks but won't start!
(Started a couple of times, but would either stall by itself, or immediately after touching the accelerator)

Pump is working properly, and fuel delivery rate is good.
Distributor and rotor were replaced by dealer 5 months ago.

Also I connected one plug to HT lead and earthed with a jumper lead, cranked the engine and there is blue spark, although sometimes none can be seen.

Jack 5 of diagnosis socket showed battery voltage, and voltage difference between 4 and 5 is 0 volts.

What could be wrong?
Could it be the igniion switching unit(002 545 26 32)?
Can anybody help me narrow down the problem or give me some additional diagnostic help? Thanks.