1994 Saturn Appears to be running to fuel rich & no temp

I appologize, but this will be long. I have a 1994 Saturn SL SOHC 1.9l that is going through gas like it is going out of style. I drive 40 miles a day so this is getting quite expensive (half a tank every day and half.) I have already done a couple things that I thought would help, but have had no luck thus far. I changed plugs, wires, fuel filter, Coolant Temperature Sensor(CTS), air filter, and ran it with fuel system cleaner with 91 octane. On inital startup the engine acts like it is flooded, by sputtering and finally idles at about 1500 rpms and leaves a black spot under the exhaust pipe. I do not have a "check engine light" and was told running it through a scanner would not help identify the problem. I was wondering if you think that the O2 sensor could cause this or if there is something seriously wrong with the power control module? Another thing while changing the CTS I left it unhooked and started the engine three time and let run for about three minutes and still did not get a "check engine light", but the light works. As for the Temperture gauge on the instrument panel, it is pegged below the "C" and only moves to the "C" after driving 20 miles or so and never gets above that. I forgot to add before but I did have a mechanic look at the car back in august after it overheated, could this be the cause of all my problems? Any help with these problems would be greatly appreciated. Thanks JP