Won't start

I have a 4.3l S10 that does not wanna start after sitting a little while. I have got to hold my hand over the air intake and hold throttle wide open while someone cranks it over. I have checked fuel pressure(72) I have changed to coolant temp sensor for computer I have changed to crankshaft position sensor an nothing has worked. It has spark just spits and sputters while trying to start and try's to run backwards after leaving up the key pops back through the air intake. I need help. Clueless at this point. Put on scanner and cp sensor was only code shown