Trying to diagnose a problem here. Every now and then when I start my truck it won't hold idle without me putting my foot on the gas. It was real random before but now it does it 1 in 3 times I start it. It's only at idle though during acceleration it runs like a raped ape and never skips a beat. Before if I would do a very hard stop the problem would go away. In the past two months I've replaced the pcv valve, fpr, fuel filter, and replaced the fuel pump with a brand new Delphi unit and none of that has solved the issue. All vac lines are good I'm almost leaning towards a bad fuel pump I've checked all wires on top of the tank and they are all good. What do y'all think?99 silverado 5.3 headers tune efans built trans 2600 stall

 

It sounds more like the IAC. I would try cleaning it on the throttle body. Sometimes carbon builds up in there and can restrict things.