2002 SL1 Temp Sensor?

Hi:

Need some advice.

I have a 2002 SL1 that developed a problem with the temp sensor around
2 weeks ago. Temp gauge needle fluctuated wildly in both directions
but mostly going down, then back to normal, sometimes dropping all the
way down to the "cold" setting just for a second. After a day or two,
Service Engine Soon light came on. I took it in for service at the
dealer, they said they replaced the temp sensor. It ran absolutely
great for about a week.

Then the gauge needle starts fluctuating again, just a little at first
and then within about 2-3 days it's back to the way it was before they
replaced the sensor. I also noticed the car was hard to drive, as it
sometimes gives it too much power when at a stop (like a light) and
it's all I can do to keep foot on the brake. When moving, sometimes it
was sluggish and didn't want to go. I am guessing this had to do with
the car's computer trying to compensate for what it thinks is the
engine being cold for a short time, when really it is not cold. The
SES light also came on again. So I take it in to the dealer. This time
they said they cleaned corroded connectors related to the temp sensor,
replaced a leaking battery and fixed a rear tail light. I don't think
whatever they did had any effect on the real problem (other than the
SES light is now off again). The temp needle is still spiking back and
forth, and the car is sometimes hard to control (either wants to go
when I am stopped, or doesn't want to go when I am moving). I don't
know how else to describe it, but it just does not run well at all. I
could tell immediately, but when I picked it up the service shop was
closed, or I would have just turned around and let them have the car
again.

So I am looking at taking it back again to the dealer for the 3rd time
(it's under warranty, so I am hesitant to take it anyplace else).
There's only one Saturn in my town, the next closest is in
Gainesville, Fla, 155 miles away, so I am trying to avoid having to go
to a different dealer although I could try that. I'm not sure if/how
much damage it may be doing to the car to drive it like this, which is
another reason I hate to set out for the Gainesville dealership.
Though if it cannot be fixed here I may be forced to try another
dealer.

I presume a few days of it running like this, the SES light will be
back on. So I am thinking tomorrow (Monday) morning I will call the
local dealer and make a service appointment. Am I thinking right to
make the appt before the SES light comes on? Seems to me it would be
better to do that. I just wondered if anyone knew of anything I might
tell them that would steer them to a permanent fix for this problem.
Is there anything I might tell the service people here to look for? I
am in no way mechanically-literate. Thanks just for reading this far.