I have a Honda Civic LX 1994 that stumbles on acceleration.  It seems
to be worse when it is warm.  It feels like only one of the cylinders
misfires while accelerating, making the car lack power and vibrate, and
once the RPMS get high enough, at around 3000RPMS, the misfiring
dissapears.  Nonetheless, it is a combination of the engine load versus
the RPMs, I can get it to stuble at any given RPM setting, if I press
on the throttle pedal too hard. Here are the parts I have now replaced:

Entire distributor, including the cap and rotor.
Spark Plug Wires
Spark Plugs
Fuel Pump and fuel strainer
Fuel Filter
Fuel Rail
All 4 Injectors
Fuel Regulator
Air filter

I have checked the TPS with a multimeter, 0.5V at closed throttle and
4.5V at full throttle smooth transition in between.
I have tested the MAP sensor with a hand vacumm gauge and a multimeter,
sensor is all nominal but here is the chart if anyone cares to look at
it:
0psi    2.80V
5psi    2.34V
10psi    1.86V
15psi    1.39V
20psi    0.96V
25psi    0.52V
I have tested the fuel pressure, pressure is normal.
I have tested the O2 sensor with a multimeter and propane torch. Again
it seems to be normal. I have also disconnected it from the car and
driven it without the lambda sensor, still the car behaves the same and
stumbles.
I have checked the timing with a timing light, and the timing is right
on according to specification.
The ECM reports no trouble codes.  The ECM reports no "Check Engine"
light while driving, although the car stumbles wildly.
I am running out of ideas... can anyone think of anything else I should
check or that could possibly be the reason for the car stumbling.

- JR