Hessitation / stumble

[Heath Vogt]

Have a problem with the new car - new to us.  1998
Sentra SE with 42,000 miles.  Checked the service log
and all the service was done at the appropiate
mileages by a nissan dealer.  The second week we had
it we started noticing a little stumble in
acceleration.  I threw some injector cleaner in
thinking with such low mileage, the car probably sat
with gas in it from long periods of time.  The stumble
got worse.  It had only been at one point in the RPM
range, now it was stumbling more than once when
accelerating from 2,000 rpm to 7,000 rpm.  I decided
good practice on a new/used car was to do a tune up,
plus the mileage was about right.  So, new plugs, plug
wires, dist. cap, rotor, pcv, air cleaner, fuel filter
all went on.  Now it's down to one predictable
stumble.  Right about 4500 rpm in second, and 4800rpm
in third.  Doesn't do it in first, and fourth and
fifth will get me a ticket.  If you're accelerating
and you put the a/c on/off it almost gives the same
effect.

Any idea's?  Next step I'm guessing O2 sensors?   I
guess it could still be dirty injectors and they just
haven't cleaned up yet.   Any guidance would be
appreciated.

Heath

=====
Heath Vogt BSME
'69 Baja Bug - Brutus "the wonder bug"
'01 Isuzu Trooper
'98 Nissan Sentra SE