high idle 95 altima

When I start my car it generally jumps to 1.5 or 2 and then eventually comes down to 1 after a few minutes of me just sitting still. Its never gone under 1 since I've brought it and sometimes ill be going like 30 mph and its between 3 and 4 rpm. When on the highway its ok but the car can be a bit jerky when decelerating or accelerating from 60 mph. Is this normal and does it affect gas usage?