1991 Ford Explorer hard to start

hi Scribbledcanvas,my truck thier is no O2 sensors anymore.its already condemned when i buy it.yesterday i try to start and it was start when i shift into neutral and sometimes it start also in park but need to move the shifter up & down.then i go to the parts store to buy the transmission range sensor,but i take the old one with me to compare with the brandnew one.my truck is 1997 model but the partsman told me that my transmission range sensor is for 1993 model,before i buy this truck the owner told me that they replace the transmission.or maybe i have PCM problem.