2003 Chevy Silverado low and surging idle.

The vacuum loss will do that. Try removing the air intake at the throttle bore, with key on(if no throttle cable) have someone hold the gas pedal to the floor and clean out around the butterfly int hethrottle body. Coking will buil d up in there and can cause low/erratic idle. There is no Idle Speed Controller with a Drive-by-wire (No throttle cable) vehicle. So the coking will reallly mess with them. If this doesnt fix it, you may have a slow motor on the throttle body which requires replacement of the entire unit. Also be sure the tune up is in good order, a slight misfire can cause low/erratic idle as well. But cleant hethrottle bore for sure