93 Trans Sport, ECM a bit crazy

Ok, this is pretty much how everything began. One day the van simply wouldnt start. It did ran fine before and no indication from ses. But all of a sudden, well here we are. The codes iv'e got is 18 and 42, but when I run in diagnostic mode, entering and going out of diagnostic mode the car some times loop the init code 12 for eternity it seems. And then some times it will present the init perfect by signaling 12, 3 times followed by 18 and 42 and occasionally 17. Should i just change the crank sensor and spark plugs and pray or send the ecm to the junk yard? Im pretty stuck here. Any suggestions? any at all would really be appreciated. It's a 93 Trans sport 3.8V6