Jaguar Repair: Runs 2 minutes then dies, propane torch, electrolytic capacitor

Question
'85 California Jaguar VDP (XJ6) with just over 108K miles.
This all started when the amplifier module died.  I replaced the module with an AC Delco D1906.  I did not change the electrolytic capacitor or the zener diode in the ignition amp.
The car starts right up and runs at about 1050 RPM, but when the AAV starts to close, it dies.  This takes about 2 minutes when started cold.  It will die at any temp as soon as RPMs drop below 1050.

If I move the AFM flap fore and aft through about 15 degrees there is no change in idle speed.  If I disconnect the CTS it dies instantly.  If I short the connector to the CTS, disconnect the oxygen sensor and prop the throttle open enough to maintain 1050 RPM it runs "forever".  The CTS has 2.5K ohms cold (65ish F) and 240 at 190ish.

Using an unlit propane torch, I can introduce propane full blast directly into the AFM without any apparent effect, but then hardly anything causes a 1050 RPM "idle" to be anything other than GREAT.  Similarly, I detect no RPM change when directing propane along the vacuum lines.

I have cleaned all the underhood electrical connections having to do with fuel except the ground bundle on the intake manifold.  If I drive the car and keep the RPMs at least 1050, it runs normally, so I doubt that there is any fuel pressure/delivery or ignition problem.  The plugs, wires and coil were changed at least a week before all this happened and I'm reasonably certain that the spark is fine.

Can you suggest a course of action, please?

Answer
Hi John,

That is a puzzle because when you supplied propane and got no response, that would make me want to start from scratch and check manifold vacuum and run a compression test on all cylinders (throttle open)

On most odd failures on any car I believe when you change the amount of fuel applied to an engine and you get no response it is not a fuel related problem. Especially when you did TWO different fuel supply tactics, AFM and Propane.

I found because of the design of the intake manifold on a ser III, that if you have a leaking intake valve, it will destroy manifold vacuum at low RPM in the whole intake manifold. So any time I get one like you have, I first test manifold vacuum for low readings at close to the cut off RPM and watch for large pulses in the vacuum.

Howard