GMC/Chebby 2.8 idle problem

If it,s a 2.8 TBI motor,they have TBI base gaskets problems,fuel regulator spring rusts out,the fuel pump should be putting out 12.5-15.0 LBS of pressure.If it,s a high mileage motor,timing chain wears out,as it,s a nylon gear.Have seen cam lobe problems as well.Do check the IAC motor,by removing the connector and seeing if it makes a difference.The intake manifold gasket splits open after awhile and cause a leak also,mrmopartech