Intermitent no cranking, or cranking and no spark...

Okay guys.. My rig 1989 XJ 4l AT... Purchased this rig yesterday. Last thursday I went to go look at it. It wouldnt turn over. Had to bypass the starter relay and then use a starter button to get it to turn over. Used the bypass to crank the engine and got it to fire. It idled horrible at first, but due to a vacume leak (the map sensor had came unpluged from the tb). Then It spat and studdered. Then died. Messed with really nothing, then tried again, got it to fire ideled up to temp could put it in gear (load the engine) wouldnt die.. By all acounts was running good. Made the guy an offer, calls me back I go to pick it up, asuming it will run good and drive me home. But to no avail. It will now turn over with out the help of the bypass, but wont even budge to fire. Turns and turns but no spark. What could go bad in a matter of two days to cause my delima... argh... Help!

sounds like the cps and nss are both bad. nss will cause no crank and cps will cause no fire.