There is one of two problems - not enough spark or too much fuel is being delivered.
Is the Check Engine lite on? A trouble code would give an indication of a place to start looking for a problem.
Is the problem different when the engine is hot or cold?
The temp sensor was probably sensing a cold engine when it wasn't cold and causing a running rich condition when the engine was warm.
If you pull the spark plugs and all are black and sooty or wet, then the problem is across all cylinders and points to something common to all, if only one plug is fouled or wet, then that cylinder/plug/injector/plug wire/etc is the culprit. All plugs fouled points to a control problem like coil/oxygen sensor/etc
I would start with a fuel pressure check to make sure that an injector isn't leaking. If its a throttle body injection (TBI), it may be possible to actually look down into the TBI and see gas leaking(engine off!! key on), but a fuel pressure check is more reliable than looking.
I would also check the ignition wires/plugs/cap/rotor etc. The coil can be checked with an Ohm meter. I'm not sure of the correct resistance, but it is in the Haynes manual I used on my '94.
The Oxygen sensor can also be checked with a resistance reading.
A vacuum leak could possibly cause the condition, but a vacuum leak usually causes a rough idle and not much more.
There are other possibilities, but these are some of the most common causes of the condition and the easiest to check.
Good luck. I would be interested to know what you find out.