1998 Ford Taurus starting problem

Driving from Ontario to California, car wouldn't start after 5 days on the road. Cranks fine, oil fine, fuel fine, fuel getting to engine, got a good spark. Sprayed some QuickStart into the throttle and that works to start the car, which runs smooth at that point. Mileage running about 20mpg on the highway. Haven't taken it in yet, but any ideas on what might be the problem? First time in the car's life that it has had this problem, although the Service Engine Soon light has been on permanently for more than a year (mechanic back in Canada said it is not something to worry about).