It sounds as if you are having a problem with the CPS/Crank Position Sensor....I take it, you must have a 97/03 Grand Prix and that will cause that kind of problem and wount throw a code.Most dealers have a problem detecting that

.It is located behind the harmonic dampner.Here is a pic of the part and the parts cost is about 30 bucks on-line or around 45/50 bucks thru the dealer
You must pull the passenger wheel, fender lining, both belts. Get a big impact wrench 400-500 ft-lbs and spin off the crank bolt. Get a harmonic balancer puller and pull the crank pulley/balancer assembly. The CPS is a plastic piece with a weatherpack connector going to it located just behind the pulleys. there a plastic shield around it that must be pulled as well. Takes about 2 hours