Ok. So...

A long time ago, in a city far far away, overnight the air became
frigid-the years first frost glazed cars's windows.  The following
morning, trouble began.  When the car was in park, the idle would be
somewhat rough.  When it was in drive, the idle would be more rough.
The roughness would smooth when the car accelerated, but the car would
not accelerate without hesitation.  I did a couple of things, and the
problem went away; however, it's unclear if anything I did had any
effect.  I changed a spark wire, and dropped in the tank some dry gas.

But the problem came back.  I don't remember the relative temperatures
as keenly; I do remember it was cold, and I do remember that the
problem again precipitously went away after I did something.  I took
off the air filter housing, checked my air filter, and replaced its
housing; the car had been running for a while.

The problem came back.  I don't remember the temperatures, but I do
remember it was cold.  Without doing anything, the problem went away by

the following morning.  Then it came back.  I changed all the spark
wires, and replaced the filter-which I think I may have been improperly

replaced the aforementioned time I checked it.  I think it had been
replaced cocked, not forming a seal.

The problem went away, again precipitously, but only after the engine
did more driving.

In Buffalo two nights ago, the temperature, after having been
unseasonably warm, dropped dramatically, and it snowed.  Last night,
the temperature still being (more usually) cold, the problem came back.

And again, it came back precipitously: After the car had been sitting
for perhaps two hours following a short drive, soon after I began
driving it back home, the car suddenly began vibrating at low speeds,
vibrating while stopped at lights, and from a stop the car began
accelerating hesitantly.

I had someone check the sensors once.  They said that they were
fine-that they had plugged in a diagnostic tool and read the sensor
outputs, and that they were correct.  But this same person was
retarded, so he could have been wrong.  (When I drove my car away after

he had done his work, I noticed the problem was worse, and then noticed

he forget to reconnect two of my spark wires.)

There is no check engine light:  there never has been.  When the
problem is active, there is pungent, more voluminous exhaust.

My car is a 1995 Chevrolet Lumina Sedan, 3.1 V-6.

Thanks alot,
Sean.