My 98 chev 1500 pickup with a 5.7 liter has a high idle.

Before thinking about other components, you simply must restore all components to proper position, including plugging in disconnected sensors. A disconnected MAF sensor will prevent the processor from getting the crucial needed data from that sensor to provide proper air and fuel mixtures for proper performance. Diagnose and replace the sensor as needed in accordance with your rough running concern, then, recheck operation of the high idle. Engine vacuum leaks can cause a high idle as well, but guessing is just simply not an option. Start with proper testing.