The "missing RPM signal" points to faulty wiring between the EZK spark controller and the LH2.4 fuel controller (I'm assuming because you didn't say you have regina, and I think that used Motronic, not EZK)

It miiiight be a failed hybrid circuit in the ECU, but I doubt it. Check that there is voltage running from Pin 1 of the LH ECU to ground. I had about 0.7V last time I checked, if memory serves. I don't remember/know anything more about the signal between the two.

Pin 17 of the EZK feeds a signal to Pin 1 of the LH to tell it that the EZK is sending spark and the LH should send fuel. These are literally two separate computers, LH for fuel maps, EZK for ignition timing, and they are connected and synchronized by a signal from one to the other. The wiring runs from the left footwell above the gas pedal to the right footwell against the wall, where the EZK and LH are respectively located.

Good luck!