Have you tried to remove the air inlet tube to the throttle body and clean all black deposits out of the throttle body? If not, here are some instructions on how to do this.

The throttle body just may be very dirty on the inside. You will need to remove the air cleaner housing that goes to the throttle body and open up the throttle blades with one hand and look in the throttle bore and see if there is any black oil deposits hanging around the inside by the throttle plates. If there is ( sounds like there is) Then I need you to buy some carburetor cleaner and use a old toothbrush and a rag and clean out that throttle body the best you can. You will use about 1/4 can of spray. Try not to spray too much down the throttle body because you may flood out the cylinders. (foul spark plugs). After the throttle body is all clean then reinstall the air cleaner housing and push the gas pedal 1/2 way down and start vehicle. It will start hard and run bad for a few seconds but then it should clear up and run a lot better,

Thank you, Tony