I may be wrong here ... but i think i read somewhere that throttle body has two sensors or two levers which regulate the fuel in take wrt to acceleration, like this
.. for low rpms .. the first sensor or motor operates and control the intake
.. for higher rpms .. the second one takes over
it is somewhat like the low speed or high speed circuit of the carburettor
.. now you need to search and find details on net
IF ABOVE IS TRUE
then either the motor linkages in throttle body have not seated properly or its one of the motors / sensor is not working
to be precise he high speed circuit is not functioning