My 97 Audi won't start when I gas up. It starts hard. If I keep the gas throttled and get it in gear I literly have to go about 6" and it smoothes out and runs perfect. Will start every time--until I gas up again. Engine light is on. It says I have a vacuum leak--took it to garage, had vacuum lines replaced, new gas cap, wires etc It still won't start after gasing