Hi to all
I have a 97 Taurus 3.0 litre with 120,000 miles
It has been maintained fairly well.

I have never had any problems, until now.
The problem happens once I am up to speed at 30, 40, 50mph
or whatever. If step lightly on the accelerator to maintain that speed,
the car repeatedly jerks, bucks, surges, or whatever name you
might call it.  It is the worst when climbing a hill, but also does it
on level roads. If I lay into the gas pedal a little harder, it stops at
once,
and everything smoothes out. Also if I put the gear selector in the second
"D" (not the usual overdrive "D") this problem never happens.

The engine seems smooth, and no service engine light is present.
At first I thought maybe the torque converter was malfunctioning,
and coming out of its lockup state. But something else is also
happening.  I am hearing a banging, popping, or rapping sound
coming from the left front area. This sound does not always appear when the
jerking occurs, in fact I only heard it about 4 or 5 times now.
But it started at the exact same time as the jerking problem.
The noise is quite noticeable somewhat like a sharp rap. But the noise
happens
only once. What I mean is it is not a rap rap rap, but just a "rap"
It reminds me of the sound of a large stone hitting the windshield,
(except more by the engine transmission area).
Also to note, this noise DID happen when I had the gear selector in the
lower "D" (not overdrive) but the noise happened without the jerking.

Sorry for going into allot of detail here, but I hope it gives some clues.

Please help me to understand what could be wrong.
Thanks Mike