Two weeks to diagnose the problem? Maybe you need a new mechanic.
The black smoke on my Rodeo was caused by a bad O2 sensor:
http://www.automotiveforums.com/vbul...d.php?t=258045
A leaking fuel pressure regulator will make the engine run rich as well.
I agree with RF, the codes should tell the story.
Post again when the trouble is found.
Dale