gas pedal

first of all hello .. I have a 307 xr break owner that I bought a second hand model of 2004, recently my car started to feel like a whispering sound in the sudden load on the gas pedal, I also have to wait for a long time to warm the engine when I start my car in the morning, Do you have any idea what the reasons could be? Also, the prices of gasoline have risen so much. I think I will get LPG on my vehicle. What would you recommend as a brand? (my vehicle tiptronic gear) THANKS ..