Mine started doing same thing (and more), my check engine light was on
giving a bad dpfe code, changing just DPFE sensor didnt correct problem
totaly, unfortunately 2001 and ealier Focuses have a known fuel pump
issue that will cause this, along with a known DPFE issue (DPFE
controls opening and closing of EGR valve). All said and done I did all
the following to get it to run nice and smooth again:
New Fuel Filter
New Spark Plugs
New Ignition Coil (found crack in old one)
New DPFE Sensor
Cleaned EGR valve
New PCV Valve
New fuel pump
Cleaned MAF Sensor (carefully)
Not as bad as it sounds, DPFE was $38 at ford dealer, plugs and gas
filter roughly $20, and I bought a used Fuel pump out of low mileage 03
wreck for $20, but ended sourcing a brand new one for $80 online, PCV
valve like $4, carb cleaner for EGR valve $3, Automotive Electrical
Contact Cleaner for MAF cleaning $6 .  Everything but the fuel pump is
a piece of cake. Fuel pump is not that hard; you just got to get car
high enough to work under it. Ford supposedly has issued a lifetime
replacement warranty on Focus fuel pumps for model years 01 and 02 but
did not do a recall.

Oh yeah, this car had 61,000 well taken care of miles when all this
happened.

I would say if you haven't done so already, check to see if there is spark
coming from the plug wires. If you don't know how to do this, find someone
who does. *DISCLAIMER: I am not responsible for any damage or otherwise
harmful effects (example: death) as a direct result from you/anyone else
attempting this maneuver!*

Have engine off. Disconnect one plug wire, preferably the first in firing
sequence. Take a screwdriver, preferably a long philips (6-8"), and insert
point end of screwdriver into the plug wire, assuring contact of
screwdriver with the plug seat. Have a buddy or trusted individual crank
the engine as you ground out the screwdriver (while it is still up in the
plug wire) on something like the engine block or frame (if it is long
enough). As SOON as you see/feel a spark, CEASE IGNITION START!!! Repeat
step for each plug wire (only three more!!) and the one that doesn't spark
or has a weak spark is your culprit. Or, if you'd like, take it into an
Authorized Ford/Lincoln/Mercury service center (f*** a mechanic) and let
them test your plug wires.

It may also be your plug gap. Check the owner's manual for the proper gap
on your spark plug and adjust accordingly. Also, check if it is burning
rich or hot, as this is also a cause for hesitation on start-up.take-off.