My 2001 Chevy impala will only start up if u push the gas and then only way u can let of the gas to keep it running u have to unplug a vacuum hose??
Try unplugging your mass air flow sensor and see if it runs better. That will give you an idea if it's your Mass Air Sensor. If not, you may have a bad or plugged Idle Air Control Valve. Here's a video on how to clean your valve. http://www.youtube.com/watch?v=i82s4ZfR2js Different car but same idea. If that fails to make the car run better, I would then check your fuel pressure. You could have a faulty pressure regulator. If pressure is good, try the throttle position sensor.