Start, no run condition with and 88 Cherokee.

I have replaced the crankshaft
position sensor several times with
different manufacturers. Presently
getting.4 volts at the sensor. Have
replaced or substituted virtually
every component. At one point put
in a brand new idle air control
valve and it started right up and
continued running. Success! But
only one start and then right back
to the old problem with start, but
not continue running. Immediately
shuts down once the key is
released from start, to on. The
plunger on the new idle air control
valve was all the way in when I
installed it. After I took it out, after
it only worked once, it was in the
same position as the one that was
there before. Not all the way in. I
even took the c101 apart and
soldered every connector looking
for this problem. I still think I
might have a wiring malfunction
somewhere. My local Friendly
mechanic that I can talk to and
get advice from, that I'm about to
pay money to, to fix this problem,
keeps pointing me towards the
crank position sensor. By the way,
can I get this idle air control valve
to operate by applying voltage to it
to make it go in and out? I've tried.
I can't get it to budge.