Just to be clear, there are TWO Throttle Bodies on the '96 3.5L.  Make sure
you clean both thoroughly and then do a power reset by removing the battery
cable for a minute or two when you are done.  You also don't say when the
vehicle was last tuned. At it's age, regardless of mileage (my '96 Vision
TSI has about 70K and I have replaced the plugs twice and the wires about
two years ago ), the spark plug wires should also be replaced assuming they
have not been to date.  I agree on replacing the air filter, fuel filter,
and the PCV (not on your list) as well.

Lastly, as preventive maintenance, the transmission pan should have been
dropped/cleaned, the magnet removed/cleaned, filter replaced and then
refilled with ATF+4 at least twice by now.  I only mention this in case you
want to suggest this to the owner keep it running well   Chrysler
transmissions of that vintage are noted for having problems if they are not
properly maintained. Make sure they drop the pan and replace the filter and
don't just do a power back flush (which supposedly gets all the fluid, but
leaves the dirty filter, used clutch material, and debris in the pan.

Good luck.  I suspect the rough idle is from dirty TBs and possibly a
plugged air filter.  Assuming much of this maintenance is due anyway, I'd go
ahead and do it first to see if it solves the problem.  If not, then take
the advice and get the error code read.  It could be an O2 sensor or the EGR
as well.

Bob

Thank you all very much:
I plan to scan the codes:
then
change the air filter
clean the intake(s)
replace the fuel filter
change the air filter
change the PCV valve
and then 02 sensors
----
???

Thank you all!
--
Car came in with a p0301 code- mis-fire in cyl #1;
and plug is burnt...-- reset codes,
replaced plug, cleaned intakes with seafoam,
and treated engine and fuel with Seafoam also;
running now, with no codes, and idles smoothly;
---
now it is ready for our master service job - front to back,
--

You guys are awesum!