Problem

My friends problem is the first time that happened to me today and also 3 times. The route I went to school consists of places where I have to be fast and slow. It requires shifting frequently. When shifting my foot a little too much clutch, today the engine stopped with the stop light. I pulled back the vehicle. The other time I deliberately slowed down again, the engine stopped, I stopped. This time, I started it by pressing the starter.
yesterday I set up for the lpg yesterday when the car outside the city I was in, when I set off on the ground that the car can't collect itself, I just sent it to my master today, but my master showed that there was a fluctuation in gas, he told me to clean the throat butterfly and use it for a couple of days, but the fluctuation in gas still continues.
When the LPG was installed, the coil changed when it fluctuated. Is the coil still stuck with a little money or my spark plugs are old (30000 km). Is that a problem or something else?
friends with knowledge please help

2004 307 technoplus 1.6
atiker lpg fast 5.0

After the throat butterfly was cleaned and boarded in gasoline, there was an improvement.