[mcfe]

I am guessing it drives fine on gasoline? To me it sounds like the car is adapting to the running of LPG and is detecting either too lean or too rich and is changing injection times WHICH ARE INTERCEPTED by the LPG computer, which affect your lpg system. That or the LPG system is doing some adapting of its own.

I would look at STFT LTFT values just to verify between LPG and Petrol in real time of course. You need to figure out why the car is misfiring e.g too much fuel and is causing it to choke or too little and is trying to burn just air. Perhaps the pressure of the LPG system is at fault.

This is just my theory of course so don't take it as fact I could be way way wrong here.