You'll need to take out the bottom 4 screws. You'll need a fairly long/large eyeglass screwdriver to get them. Such as the one farthest to the left in this image : http://www.allproducts.com/tool/ark/Product-200718134246.jpg

I'll take a look at mine and see if I cant post some images to help.

Edit:

Just took mine apart and put it back together successfully (and voided yet another warranty ) and will say that there's not much room in there so I hope you have some small tools. The one above plus tweezers and a desk light come in handy.

Disclaimer: If you choose to take the quadrant apart you risk permanently damaging the quadrant as well as voiding the warranty. You probably wont damage anything.. but you might so I say this. You did it of your own free will and I assume NO responsibility!

Ok so first take out the 4 screws on the bottom of the Quadrant. There should be 2 small screws in the front and 2 long screws in the back. Next take off the base, this requires a little prying to get it off, but it comes easy once you get it started.

Next, Take out the small screw on the back, its on the side where the cord comes out. Its the upper hole when the quadrant is upside down (I already took it out obviously) and its plainly visible when you look at it.



Then on the inside you'll see the below plastic piece, just slide it out.



Next you'll need to take out these 4 screws that hold in the circuit board. The one under the LED is very tricky as you'll need an eyeglass screwdriver that can fit in between the prongs.



After you get that free, go to the back of the throttle you want to work on, (in this case the Z-axis) there will be two screws in the back at the bottom holding it in. They are a pain in the @$$ but it's possible.



After that, It should slide out fairly easily. But to get it all the way you'll need to force it the last inch as there's some plastic sticking out of the lever that holds the black throttle cap on.



Chances are that this is where your problem is. Just make sure the 3 wires going into the Z-Axis are all solid and aren't touching each other.



You probably wont need to go this far, but I went ahead and took apart the housing for the throttle lever. Its a VERY simple system.

The below is the axis of the throttle lever, on it you see a small rectangle protruding from the lever.



That rectangle fits into here which moves the Servo (its not really a servo but I cant remember its fancy name.)



Here you see the outside of it, check again to make sure the wires are all connected and not touching each other.



I don't see any physical way for the throttle to be jumpy unless there's a short on the chords. Just make sure that all the connection points are separate and aren't touching or loose. If you do find them loose it will require re-soldering the connections.

Put everything back together, pull up the control panel and make sure everything is working!

Hope I was able to help in some way