93 Suburban

[Festus611]

I have a 93 Suburban with the 350 with TBI. What can do as far as the fuel air mix (if this is even the problem). It seems to be running too rich. When I travel on the highway for a period of time at the same speed and go to accelerate i get a puff of black smoke. Almost seems like its getting too much fuel thats not being burned off. This doesnt happen with normal road driving. Also along with that, if it puffs real bad I get the "service engine soon" light until it clears out, then it turns off. I have tried new plugs, wires, cap, rotor, checked the timing, idle air control valve, air filter, one of the fuel injectors, egr valve was replaced about a year ago. I am at a loss. Could it possibly be the throttle position sensor. Since thats one of the only last things I haven't done. Thanks.