Ford Repair: 99 Villager Speed sensor?, service engine soon light, sensor error

Question
Hi. My Villager has several things which seem to go down to the same problem. First I noticed that it wasn't shifting from time to time into the 4th gear. Second O/D off light flashes on the time of start up, I have to turn the ignition back off and on and then it won't flash. Third Service engine soon light came on - Speed sensor was loose and has been fixed. Forth service engine soon light comes on again same reading speed sensor error - service engine soon light has been deleted. Fifth rpm on about 2000 when in P or N (result going into D or R doesn't really sound healthy) and service engine soon light comes back on, still having the O/D off light flashing. Yet, my speedometer works just fine. Can that be all because the speed sensor is bad?
Thanks

Answer
It sounds like more than one problem.  A speed sensor will not affect engine idle speed.  It would, however, cause the flashing "o/d off" light and "check engine" codes.  It's possible that the drive gear for the speed sensor is bad, or even the speed sensor wiring.  Are there any other codes?