I assume you've deleted your joystick calibration file and recalibrated in AH? if not this could be the cause of spiking
Also recalibrated in windows? always 1st thing you should redo
checked for joystick driver updates? always worth a try
basically it could be one of several things causing this:
if its a usb joystick it might be worth checking for updated 4 in1 via drivers (if your motherboard is via chipped version)
if its serial cabled joystick then it could well be a fault with your joystick controller on your sound card.They often 'give up the ghost' and start causing huge spikes in movement. have you got an old soundcard ? try putting it in your computer and testing it with your joystick.If it works you know its your port.
If it the pots then simply clean them and if it continues you have eliminated that.
lastly try any other joystick you can find and see if it happens with this too in which case it could point to a problem with the AH programme or install.
try downloading the full version (latest AH) and reinstalling the whole thing to eliminate the possibility of a faulty install/corrupted file.
if it still hasnt clued you in , take a load off and just buy yourself a lovely NEW joystick to save the headaches

good luck