Just before I got the car passed on to me from my family, we had it serviced, and (stupidly) tuned by a garage which really doesn't have the know-how to do so (it runs a dual fuel system).
After a few weeks, it started backfiring on LPG (mainly taking off from lights). Back to the garage, tried to retune it, fixed for a while, then the problem came back.
Finally we went to another place. $80 and it was perfect, back to normal. The fix wasn't really very good though, cause it was just a work-around on a problem with fuel delivery (and could possibly be running the system a little too rich at low revs). The Computer that controlled the gas flow was "disabled", and the bloke said that they tend to break after around 18 months, but an econovalve would be a better more permantent solution. Tried that, but it ran way too lean. Also at this point, they replaced the MAP and Oxy sensors, not sure that it was required, and it made no difference to how the car ran, but it did cost ~$380.
Finally, we decided to get a new computer, with the idea in mind that it was still not very economical (it was actually my lead foot the whole time). Finally we thought it was back to new. After a few months, I took it back because of really poor idle at the lights (it would shudder and lose heaps of revs, and then take off would be very poor.. after one trip through the city, it lost ALL its guts, and even after an hour of freeway driving, was still gutless.) I took it back, got a free retune, and it is now compelely fine.
Total cost: $1200. Problems with this: The original computer was "disabled" but I don't think they ever checked to see if it ctually still worked by re-enabling it :(, Also, the $80 fix at the start was perfect, and it should have been left at that.
Also at this time, with all the testing of the exhaust fumes to determine fuel mixtures, they noticed petrol was running extremely rich (eg. valves always fully open). They "fixed" this by cleaning out some gunk from somewhere which was appartly holding something open. When I got the free re-tune, they said it was still running really rich (I had noticed, cause fuel consumption was still crap). So I had paid for labour for this to be fixed and it wasn't actually fixed.
All in all, a complete screw over caused by incompetence by the mechanics and blind faith by me that they knew what they were doing.
ps. avoid Carrera Automotive (croydon, vic), unless you have a LOT of money to blow
They will replace everything they see, without consulting you first, no matter what it costs.