On my Bosch distributor, there's a small rectangular two pin plug on the side for the sensor connection. The shielded cable starts right at the plug.Steve M wrote: How close to the sensor did you start your shielded cable?
Where did you ground the shielding?
Only earth one end of the braid, just find a good earth point on the body somewhere. To be safe, don't use the same earth point that the ignition module or coil uses.
I would have expected an RPM signal with the coil disconnected - unless as delco suggested you removed the power from the ignition module as well by unplugging the coil.Coil disconnected (grey and black plugs) = no RPM signal (as expected)
You could try just removing the HT lead, that would help rule out the plug leads and internal arcing inside the distributor if it stops the RPM issue.
And you might want to leave the fuel pump fuse out for all your testing until you get the RPM issue sorted. Every time the ECU sees the phantom RPM signal it's pouring enough fuel in to match.