Rough idle, stalling and no cooling fan at operating temperature.
 

I have a 1994 SL2 and I have had no real issues other than that pesky little black box in the center console that seems to control everything in the cabin of the car. But now I have a rough idle, hard to start, stalling occasionally (but getting worse everyday) and my cooling fan comes on when I start the car. Once I drive it for a mile or so the fan turns off and never comes back on. But the hard starting, idling issues, and stalling continue. Is this all because of the engine coolant sensor? ( The one that is on the car is still the great mistake of Saturn and is definitely plastic.

Sure sounds like the ECTS to me, but I'm not a mechanic. And I'm referring to the one that's on the drivers side of the car and has the squeeze connector. You really need a brass tipped one. Is there a Saturn friendly GM dealership in your location? If so, get one along with the new pigtail from them. Probably be around $50. BUT, the first thing you need to do is have it scanned for codes. You can pick up a cheap scanner at Walmart for about $20. I have one of them and it works great on my Kia Forte and my sons 2013 F-150. Get your codes and either look them up or post them here.

The cooling fan coming on when you start the car if not with the air conditioning already engaged (the fan always should come on when the air conditioning is engaged if the system is properly charged) I believe is a Fail-Safe behavior when the ects or related wiring causes the reading interpreted by the PCM to be crazy hot. Either the sensor itself is shorted internally, there is crap between the pins where the connector attaches, crap meaning corrosion, or there is a short in the wiring between the ects and the PCM terminals.

Along with the fan turning on, the PCM thinks the engine is very hot and is probably leaning out the fuel mixture to the point that it is difficult to start since this is the opposite of the equivalent of a choke engaged on an engine. Similarly, their fuel mix is just all wrong. So the engine behavior is not unexpected.

I will check for corrosion on both the connector and the ects pins, then check the wiring for chafed wires shorting to each other. Measure the resistance across the ects terminals. Be sure not to let the probe tips touch. If you read zero it is shorted and needs to be replaced. Do a continuity check as best you can from the connector terminal down the line towards the PCM. It is often very difficult to locate issues at the connector terminals themselves.

If you have never replaced this and it is the original factory one, go ahead and replace it and the pigtail in addition to anything else that needs to be corrected. It has been replaced with an updated all brass design