1993 Sentra SE-R new owner-HELP!!!

[nick saettel]

I have a 1993 vail white SE-R 5 speed.  The car has
just under 85,000 original miles on it.  Here are the
facts:  The previous owner (it is a one-owner car) was
a single mother of two, who seldomly performed routine
scheduled maintenance.  Car is cosmetically in good
shape, but has some small defects aside from the
running problems (i.e. rusted and broken battery
hold-down, worn carpet, sun cracked center
armrest/console lid, etc.). When I bought the car it
would not run without holding my foot on the
accelerator.  Upon futher inspection I found two
cracked points in the distributor cap.  To solve this
I did a normal tune-up (replace the spark plug wires,
spark plugs, air filter, fuel filter, PCV valve,
distributor cap, and rotor button).  This allowed the
car to run without accelerator assistance, but it was
still running rough and jumping at idle, so I looked
on SE-R net for common fixes to common problems, and
thus, I removed and cleaned my M.A.F. (mass-air flow)
sensor and T.B. (throttle body).  This produced a
somewhat smoother idle, however sometimes shortly
after start up, it still jumps slightly and is
hesitant on all acceleration, especially at low
(off-the-line, 1,000-4,000) RPM's.  I saw on SE-R.net
that this could be the result of a plugged EGR system,
so I disconnected my EGR and ran the car to see if
this was the culprit, and it still ran the same.  The
car never stalls on me, but on rare occasions, it
comes close.  I have also noticed on my last three
tanks of gas in mostly mixed h.w. and city driving
that my total fuel economy is between 21-23 mpg by my
best estimates which strikes me as poor for this car.
I did notice that when I was installing the new rotor
button that when I went to install the old (I should
have invested 15 cents for a new one!) retaining screw
back to the new rotor button that the head of the
screw boke off leaving very, very slight play between
the button and the distributor shaft.  Could this
mishap on my part cause all of my engine woes, or is
this the result of some greater problem?  Any feedback
or information on this matter will be sincerely and
greatly appreciated, as I am falling in love with my
SE-R  more and more every day, and would like to have
it running as well as it should at this mileage.
Thanks again so much!