Simple, easy and (relatively) cheap problem to fix - change you fuel filter.
Several bad batches of fuel from the same station could have picked up
enough junk (dirt, sediment, algae, etc.) to easily clog your stock filter,
and poor idle is the first symptom.  If you had any appreciable amount of
water in your filter/seperator unit it would turn on the "Water in Fuel"
light on your dash.

Although a good fuel conditioner can be beneficial, don't go overboard with
it.  My personal experience is that I have the best results when I use it on
the lean side.

I also recommend using a second (auxillary) fuel filter with a 2 micron
rating, and insisting on the newer model stock filters with a 2 micron
rating (the older OEM filters had a 10 micron rating).  There's an easy to
mount Racor aux fuel filter kit available at www.lubricationspecialist.com.

Cheers - Jonathan