That vintage 5.0L V8 occasionally developed a leak between
the upper and lower intake manifolds which would result in
the lean codes and sometimes a high slightly unsteady idle.
One problem area for external vacuum lines is around the
back of the intake manifold going to the vacuum canister
which is a reservoir for the HVAC and the EGR system.  If
you have had the vacuum connection off of the vacuum
reservior, make sure you check it for proper connection.  It
can be connected wrong  causing at least some of your
problems.  This condition is not visually obvious because of
the way Ford made it.  You can sometimes find the intake
leak by spraying around the joint between them with
carburetor cleaner or WD40 or a similar combustible spray
with the engine running.  When you hit the leak area, the
engine idle will change.  I do not recommend using anything
like starting fluid or ether as it can both damage the
engine when it is drawn in and ignite causing you serious
burns.

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