if it is randomly cutting off, you need to figure out if it is ignition or fuel. when it is not running, check ignition. keep a spare plug handy to make it quick.
for ignition, usually random dieing is the result of heat and about the only way to fix it is to what for it die completely (sucks) or swap CD, coil and possibly dist. (one at a time)
for fuel, look for fuel pumps, relays and dont forget the speed sensor.
you can go here for my explanation of the fuel circuit
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/615670-fuel-pumps-not-working-ign.html
i hope this helps