Cheap, easy tip to address most likely P0171 cause:
First, check your Baro reading on your car chip if possible.  It should
read 159 Hz at sea level driving conditions.  It should read about 140
to 145 Hz if you were a mile high.  I usually see 158 on a properly
running Ford where I am.  If the number is lower than it should be, do
the following...
Remove the mass airflow sensor from your intake duct. Disassemble the
halves, there should be two tamperproof torx screws, and locate the two
sensor elements deep inside the plastic extension that hangs down in
the airstream.  Clean them with electronic spray cleaner or brake
clean, carefully touch a qtip to them without applying any significant
pressure, blast with cleaner again, and air dry with light pressure if
possible.  Now go on a drive.  Floor the car for a few extended runs as
long as you can safely and legally.  Now check the Baro reading again.
See if it is higher now.  If it is exactly the same, try a few more
power runs.  The ECM needs to see wide open throttle while under actual
driving conditions to infer the barometric pressure.  What you are
seeing on that data list is the ECM's reported MAF frequency (to put it
simplisticly) that correlates to the pressure in the intake duct when
the engine is not adding or subtracting any from atmosphere (in
theory).  It works for Ford, but their MAF design is one that needs
periodic cleaning to keep it reporting accurately.

Common P0401 cause on some 4.6, I don't know when this was corrected,
but 1995 engines may still have this problem:
Remove the throttle body, check the flange surfaces of the throttle
body and intake manifold for coked up crud.  Clean it out and make sure
that the tubing/passage behind the EGR valve flows air freely as well.
Then make sure the EGR VSV operates and that the EGR valve does infact
open.

Toyota MDT in MO

This is a definition of the P0401 code for a 99 Taurus...should be
similar for your car:

"The EGR flow rate test is performed during a steady state when engine
speed and load are moderate and EGR vacuum regulator duty cycle is
high. The monitor compares the actual Differential Pressure Feedback
EGR circuit voltage to a desired EGR flow voltage for that state to
determine if EGR flow rate is acceptable or insufficient. This is a
system test and may trigger a DTC for any fault causing the EGR system
to fail. The DTC associated with this test is DTC P0401.
DTC P1408 is similar to P0401 but performed during KOER Self-Test
conditions. "

The DPFE module  (about $50-ish) is a known common failure on many
fords.   They get crudded up with exhaust carbon, etc...and get sick.
I replaced the flex hoses too...

I suggest you get a subscription to Allldata or get a quality manual
(Haines, etc)...there you should find a complete description of how
the EGR works and troubleshooting procedures.    I've been using
Alladata for about 4 years now...pays for itself in $$$ saved every
year...not counting the time and  aggravation saved!

Best of luck!

--Don Byrer

Don Byrer KJ5KB
Radar Tech & Smilin' Commercial Pilot Guy
Glider & CFI wannabe
kj5kb-at-hotmail.com

"I have slipped the surly bonds of earth; now if I can just land without bending the gear..."
"Watch out for those doves...<smack-smack-smack-smack...>"