Heat/Temperature gauge The temperature gauge goes up slightly when the car is sitting still, but when I am driving the temperature gauge goes down completely. The blower works great, but the car doesn't get warm. What is the problem?

SOURCE: temperature gauge fluctuating surges

That sounds like the classic symptoms of a cracked ECTS (temperature sensor). It is located on the head near the upper radiator hose and battery. You will see two wires (likely a yellow and a black) going to a small sensor hiding in a little cubby hole. If you pull off the connector (there are two points that if you squeeze it lets the connector come off) you will probably see that the connector is corroded because the plastic body of the original ECTS cracked and let a small amount of coolant into the connector. The ECTS is only about a $10-15 part, be sure to get the updated one with a brass body. Then the hard part is you will likely need to get a new connector, one of the best places for that is a junk yard, the temp sensor for the transmission and the air temperature sensor near the air filter use the same connector. When putting this in be sure to solder the connections and cover that with heat shrink tubing. There are video's from Richpin06A on youtube that will show you how if you have any doubts. The saturnfans forum is a great place for info too,
http://www.youtube.com/watch?v=yQx84-93WkE&feature=related

SOURCE: problem with idle

engine coolant temp. sensor is probly cracked it will cause the idle to race, car may smoke, and at time could be hard to start.. It is about 15 dollars, and it is located on the right side of the head if you are looking at the engine.. pull it out you will be able to see if the tip of the ceramic tip is cracked.

SOURCE: saturn sl2 temperature gauge normal reading?

mid range of the gauge is normal keep in mind the full sweep of the gauge is only about 40 degrees the fan turns on at 220 degrees