The air duct just slides off the throttle body. Its just press fit on there really tight. It should take both hands to get it off. Then, in the throttle body, you'll see the maf screen. There is a split ring holding it in, but it wont just fall out when you remove the ring. I buggered mine up a bit taking it out to clean my throttle body. I then realized it would have been much easier to remove the maf sensor from the TB and push the screen out from the rear.
My car was doing something somewhat similar and it ended up being a vacuum leak. Check all your hoses for cracks, splits, or pinholes. Unplug the maf sensor and start the car to see if it still has the problem to rule that out.