guys its going to depend on what sort of start problems you have
if the engine kicks over and you are ready to release the key because the starter is turning too fast, then the engine stops, this indicates low fuel pressure, the only reason the engine appears to kick over is because your cranking it and giving it fuel, so it fires slightly.
if the engine starts perfectly but then just dies (and you can avoid this by holding down the throttle), then as jbolger said its probably the ISC motor.
check your fuel pressure, not from the regulator, from the pump. If you havent replaced the fuel pump in the last 5 years then this could well be your concern.