1994 buick Le sabra hard to start it has spark when start it runs it smooth and strong shut it off it wont start ?
On a 28 year old vehicle, it could be anything.
Still with the basics: air, spark, and fuel. Sounds like you have spark and air. Could you have a weak or dying fuel pump?
On a GM, fuel pump would be my first suspect. They can be hard to start like any electric motor but once started can run fine. Lots of other possibilities though but listen for the fuel pump running or not when it won’t start. Banging on the tank with a hammer can sometimes jar it to work.