88 bronco acting up HELP

[usat212]

When I start it when the engine temperature is cold it starts and runs fine while it is idled high, but when it starts to idle down when it starts to warm up it starts bogging down like it is flooding out. It also starts blowing black smoke. If I rev it up it clears up. If I don't rev it up and just let it continue to bog and miss it will do it for a little bit then it just clears up all at once like someone just threw a switch. After it has warmed up, I can try to rev it up high and try to get it to hold a steady RPM, (like say 2000 RPM's) it will just rev up and down up and down like your mashing the pedal and letting off. I unplugged the O2 sensor and the revving up and down went away but it still boggs down like it is flooding and blowing black smoke after you start it. Now with the O2 sensor plugged in it will idle pretty steadily unless you try to hold a high idle. Also when you try to hold a high idle it will at first then the up and down start. I get a code 41-oxygen sensor indicates system always lean. I have replaced tranny vacuum modulator( it was leaking and had tranny fluid in the vacuum line), fuel pump relay, O2 sensor( the wire was against the exhaust pipe and had melted and most likely grounded out), coolant temperature sensor, fuel pressure regulator,. I have had the ignition module and MAP sensor tested. I have cleaned the Intake Air Control Valve anyone know what it could be??