Got a VZ Commodore (as well as the dattos) which had a dodgy idle when on gas. Its the Holden Factory fitted Impco /BRC conversion and is still under new car warranty.
The dealer said they "couldn't do gas warranty work" so they sent me to an LPG specialist. Turns out he did not have the diagnostic gear so he sent me to another gas workshop.
These guys were brilliant. Took the car in the next day and they hooked the car's computer up to the system manufacturer's computer 4000Km away in Melbourne. Found a few issues and downloaded a new programme.
Cost for this sort of service----- FREE. Unbelievable!!

So Eddie at IMPERIAL LPG in Cannington Perth gets my vote if you need LPG work

Theres a good one in Mount Lawley aswell.