How to stop ,y 1998 chevy Silverado 1500 from idling very rough to where it's shaking

Robert, have vehicle scanned for diagnostic codes. Check for vacuum leaks and if you have not done recently give vehicle a complete tune up cap,rottor,wires,plugs,filter's,etc, including injector/throttle body cleaning. Check the attached links,instruction and guides, Good luck
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Leaking intake manifold (vacuum )

Did you replace the temp sensor located on intake.

yea id definately try cleaning ur throttle body 1st. My 03 1500hd had the exact same bad idle after my battery went bad it would die at lights unless i kept foot on gas i cleaned throttle body runs perfect now took 30min cost 8$ for cleaner at autozone and theres how to videos on you tube

did you gat some gas before it started running rough ? might be bad gas. were there any other codes ?

http://www.2carpros.com/articles/engine-misfires-or-runs-rough

read this article it may help

DTC Number
P0160 DTC Name O2 Sensor Circuit No Activity Detected Bank 2 Sensor DTC Number P0300 DTC Name Random/Multiple Cylinder Misfire Detected

ICM idle control module, loc throttle body, it may be dirty, remove clean or replace, its easy..

try a new idle air control valve