Contraction and idling speed increase at low speeds

Greetings to all
I have been riding my Peugeot 306 griffe 1998 car, which has been my first car since February. It was 171 thousand km when I bought it. There was no LPG. Since the fuel consumption was too much, I got the ATIKER sequential system LPG. burns 30-33 cents a kilometer. I still think it's too much.

When I first bought the car, I replaced the oil, oil filter, air filter and cornering rods. After 4 thousand km, I had to make an oil supplement due to the loss of oil (since the oil light lamp started to light up). The technical data of the vehicle says that there may be 0.5 L. oil reduction per 1000 km. Wasn't oil change too much at 4 thousand km?

My car was running jerky while I was working. It is even noticeable from the tachometer. Spark plug cables and spark plugs have changed. There seems to be some improvement but now I have a different problem. At low speed, the car cuts gas, shakes and even stops. Especially LPG is very obvious. In addition, sometimes at idle, the speed of idling is 2 thousand.

These problems are of course the things that would require a master's hand to be touched but I am happy if I could get information from friends who had suffered my problems in the past and solved their problems.

Thanks in advance