1999 SAAB 9-3 repair Question Starting

Over the past two months I have had to have mycar towed three times. Car cranks cranks cranks and finally sputters and coughs to a start. The first time they replaced the crank sensor. The second time thet told me they thought it was bad gas that I should let it run down to almost empty fill it with Mobil and dry gas, repeat this a second time, I actually did this three times. The third time they told me I should get it out for a good run on the highway and keep using dry gas. I did this a couple of times. They have runit on their computers and tell me they get no codes. They have supposedly checked every part, wire fuse etc. Nothing. Still the problem. Onced the car starts it runs like a dream. It has also got a brand new battery, M.A. McGlone e-mail jack606@aol. Com