Rough low idle fluctuates 2001 Chevy Silverado

I had a simular problem w/ my 2003 chevy silverado 4.8lt Z-71, I also had no Engine lite or code, I took it to the dealer and paid for a diagnostic when I didn't need it, maybe it reassured the dealers but they didn't find any codes also, So they cleaned out the throttle body bore, they found some gunk inside and all around they sprayed it with some sort of cleaner and test drove it, ever since I had no problems to date, I checked everything from the battery to the starter and alternator all connections but it was the throttle body bore, start there, hope this helps. Nacmem