Mick,
Firstly congrats on getting the HPDI, they're an absolute weapon of an engine when running right but fiendishly complicated and hard to diagnose when not. There are also very very few people left in the UK who truly understand how they work!
Have you got YDS?
Have you got the manuals? If not, PM me and I'll send them to you.
Back to your problem.....have you checked all the obvious stuff first like sticking Morse cables, throttle linkages, butterflies. Is your TPS working correctly (you'll need YDS to check this). Sticking linkages would cause your problem but wouldn't explain why it resets on key-off. Dodgy TPS might though.....
PM me if you want to discuss - I know the HPDI fairly well
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