I think you will find this is Motronic 2.8.1.Even though your scope signal looks ok,it is possible the part of the signal is going to ground via the earth screen in the tdc sensor cable.Do you remember the 90s astra model that would not run properly unless the earth screen cable to the sensor was cut?The Bosch system on these is generally very reliable and tbh and if I recall the tdc sensor was the only weak component.If you are still in bother ,I have an original GM wiring diagram for this model,On paper!but I'm fairly sure it is the same as the on the Bosch esi.hth