If you take the
valve off, there might be 2 holes in the manifold.
1 from exhaust and 1 going into inlet manifold..
Quite a few diesels have the
system and they blank off the holes using a home made plate and gasket. So presumably it can be done on a petrol version.
Might be worth a look under your valve to see if it can be done.
You could then blank the vacuum connection off and see how it runs. It can always be put back to standard later.
If the relay is already disconnected, the
valve should be closed, but it could be stuck open slightly.
Is there a vacuum diaphram on the control module ??
That should be for ignition timing vacuum advance like on a normal distributor.
Have you tried running with that vacuum pipe disconnected and plugged.
There might still be enough advance built into the electronics in the control module for it to run without the vacuum.
All worth a try and nothing that can't be put back as it was.