Yes it is adjustable through the software on the Arduino but if I have just trashed both valves I'll need an alternative.
Good point on the vac booster diaphram. I'll hold on to the the spare booster from the other car in case of future problems but will dial back the vac.
I ordered a couple of these
https://ebay.us/PXbzCF but they'll be a few days coming.
In the meantime months ago I had bought a Volvo vacuum switch which might do the job. It is self contained so doesn't need controlling but also can't be adjusted, nor do I have a connector for it but after lunch I'll give it a go.
What's the worst can happen?