Speed under load fully there but in idle only up to 4000 tours

Hello everybody, I’m new here and don’t know exactly if I’m doing all this right here? The following facts: Have a V70 II Built 05/2000 T5 automatic. New candles, new ignition coils, DK cleaned. The car has an LPG installed. On petrol the engine runs very unevenly, as on 4 paws. also under load up to 2500 tours. When it switches to gas it runs completely round. What can that be? Furthermore, I can’t turn the engine in P or N over 4100 revolutions. on the track but in all the corridors it turns out full of gasoline and gas!! What can that be? Where is the error???