'93 S-10,2.8L, fast idle

My truck has very fast idle at start, then slows to only fast idle when warm. No " check engine" light, but get computer code # 34: <MAP sensor low voltage>. Vacuum reading at idle is steady at 17+ inches. Anyone have any suggestions?

Thanks,
Roger

there is an idle adjustment screw on the passenger side of the tbi....its a torx head and you will probably have to have an extension and a universal joint, clockwise is faster counterclockwise is slower