In the garage he gave code 17 ) on gas/lpg and benzine between 60 and 90 kilometers car is vibrating changed plugs, ignition, cables ran very well for3 months after that bad again, what can I do?

indicates insufficient gas flow/pressure

Try a new gas cap

as lpg expands to around 200 times the liquid state it will be difficult to calculate as how you want it
the car has a liquid tank but the liquid is converted to gas in a converter on the manifold.
basically from experience an engine on lpg gets about 75% of the mileage as if it was on petrol for the same amount of lpg in litres
talk wit an accredited specialist automotive gas fitting shop and they may be able to give you a better idea
you can work it out by filling the lpg tank to shut off and setting the trip meter to zero and then when you have done say 100 klms refill the lpg tank to shut off and that will indicate how many litres were used in that 100 kilometers

Th engine must be prroperly tuned for the LPG if this was fitted externally . If this was factory fitted please get a proper fuel setting done on the gas , check the spark plugs , the intensity , and also the timing.

If your coils/wires are on the correct cylinders then, with the truck running unplug your alternator if the truck runs smooth then you have a short inside the alternator causing change in electrical current, if this is case replace alternator.

the fuel pump may have burnt up or you may have air in the line

try replacing the fuel filter

LPG 3Y engine toyota crown comfort automatic - fuel consupmtion is 13.30litre per 100km? How can this be reduced?

I have a 1999 A6 2.8, and my car was doing the same thing. However, after spending about a $1,000.00 I took it to another dealership. they replaced the fuel filter, it was dirty from putting cheap 91 gas in the car. Once it was replaced the car ran like new. I had to replace it around 80,000 miles. Hope this helps

AS far as i understand it your air flow meter only controles your idle, not your air/fuel mixture. The mixture is controled by the Air/fuel mixture body that sits immidiatly below your fuel distributor. it has a 'tower' that reaches up to a hole in your aircleaner so you can get to it with an allenkey. To set the mixture correct it needs the aircleaner on. that screw changes the pivot point of the arm that gets depressed by the large round disk visual if the aircleaner is of. This is not a throttle butterfly, it mechanically 'measures' the airflow by being sucket down and pushing a plunger upwards into the fuel distributer increasing the amount of petrol to the injectors. You say gas as a supplement... I assume you mean Hydrogen Fuelcell. Because if your trying to 'add' instead of replacing with LPG or Natural Gas you will have a problem as LPG for example needs to ignite earlier. For example if the petrol engine fires at 6 deg BTC on petrol, than converted for LPG it needs to fire at 16 deg BTC on their original plugs (newer plugs are available that allow for an acceptable setting suitable for both fuels but all i everseen when petrol was still present when switching to LPG is an 'engine bay' fire)... But assuming your talking Hydrogen fuel cells as a supplement to try and reduce your fuel consumtion than the element that could create a problem for you is the Lamda probe (Oxygen sensor) in your exhaust as it may think that your fuel mixture is to lean and tries to increase fuel through the cold start injector or the electronic pressure regulator on the fuel distributer. I hope this will help you somewhat.