Welcome!
Some black smoke @ wide open throttle is OK, however with your other symptoms, it sounds like it is running rich. most likely an O2 sensor.
IS your check engine light on? If so, you need to pull the codes. It can be done with a paper clip.
Keep in mind that the search function is your friend, it takes some getting used to, but it can be effective.
Anyway, for checking the codes, this is from 90coug:
"Take the paper clip and on the EEC test point under the hood (On my 90 XR7 it's on the passenger side up by the firewall) jump the single wire that comes out and the black wire that sits at the bottom of the trapezoid looking deal, a picture would be better than me trying to describe this but after you jump the two wires just jump back in the car and turn the ignition on. You'll hear the fan start turning and once you hear that you know the test is in progress, then just read the flashes on the dashboard. This is for EEC not OBD
You can also start the car and run the KOER test"
Here is a link to someone that was experiencing similar symptoms:
http://www.sccoa.com/forums/showthread.php?t=84327&highlight=running+rich