Has anyone gotten to the bottom of this yet? I am also an owner of a 99 Sunfire and have the exact same issue. Mine just has a mind of its own. Sometimes it will fire right up and other times it will crank over for 10 seconds and sputter to a start. It is terrible! Mine has also been like this for over a year now...due to me and my mechanic not being able to figure out what the heck is causing it. Just this weekend I finally had to replace the starter and the battery because they have both taken such a beating from this issue. Here is a list of what I have replaced on mine and still has the issue.
Battery, Starter, Ignition, Cam Sensor, Crank Sensor, Fuel Pump, Fuel Filter and Spark Plugs.
I have not replaced the spark plug wires yet because they look fine. But we all know that looks can sometimes be deceiving so I will try swapping these out next...
Has anyone tried the Fuel Pressure Regulator like Jason/RKBA suggested?