Well my new regulator is fitted and working, and so far so good.
I think that the old one was indeed simply worn out - it had done 220,000 LPG miles, so I reckon I can forgive it being a bit tired!
When it came to setting everything up again after the regulator had been fitted some judicious remapping was needed, but certainly having driven the car home 40-odd miles, it is much much better, and certainly no oscillating.
The probelm seemed to be caused by the LPG regulator delivering gas irregularly. This would cause the car's ECU to think that either the mixture was too rich or to lean, so it would try to adjust the engine speed. But in doing so the mixture would then change, so making the ECU think that it needed to adjst the engine speed again - and so it went on, up and down!
When the system was re-configured, very close attention was paid to getting the injector speed of the LPG injectors correctly matched to the corresponding injector speed of the petrol injectors, and also making sure that the gas pressure was correct. The whole process took the best part of 2 hours.
As I say, the root cause of the problem would seem to be the fact that the system in my car was just old and worn out. However, having seen how carefully the controls software was set up again after the new regulator was fitted, I can't help but wonder if the other two problem cars reported on here simply need some time spending with an experienced technician.
Cheers
Jack
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