95 achieva runs rough

I have put in a new oxygen senor, new cat. because it was bad, new plugs, but the car still runs poorly. my check engine light comes on with the cooling fan for maybe 10 mins. does anyone know what can be wrong. also at times has black smoke out the tailpipe.
thanks for the help.

Go to Autozone and have them check for codes for FREE to make sure there is no other code stored.

You said that check engine light comes on while the cooling fan is kicking on and then the check engine light turns off when the cooling fan is off?