306 idle and stop problem

I have a 1998 model 1.8 16 v 306 recently, while my car is working on gasoline, the engine shines very hard, I can say less in gas and stop at genius occasionally I was used to gas occasionally, but also I did not have a gas throttle, and I also changed the idle engine in the gas, the car was less in the gas. gas is eating and its sank is like a decrease in the traction of my car recently. ?????