Normal sound?/vacuum leak?

Hey guys

I have a 99 1500 with the 5.2. I have only had the truck a couple months so not sure if maybe the rams just sound like this. When the truck is first started it sounds almost like a constant vacuum leak. Not super loud but can definately hear it. After it warms and is driving I can only hear it when pushing on the gas. After inspecting I found it is coming from the hole on top of the throttle body where the IAC comes in. I changed the IAC to rule that out but still the same. Is this just normal? I also notice if I decelerate, say when I come up to a stop sign, I put it in neutral and begin to brake. The rpm will jump up and down between 1000 and 2000 until I come to a complete stop. Then level out. It is a stick and would normally downshift but noticed this issue as well. Am I overreacting? Thanks for your time guys

Brandon

My 5.9 was making that sucking sound at an idle when I came to a stop. I ignored it then it started running rough at an Idle. I replaced the IAC and the rough Idle was gone but the sucking noise remained intermittently. I ran a couple tanks of Lucas Fuel treatment through it and now it almost never happens, only when I get off the freeway after an hour run.

The sucking is either the IAC or O2 sensors typically.

The idle surging is normal with the 5spd unless it wants to die. Mine has done it since new.

I definately seem to be noticing it more and more when the truck is cold. It seems to be getting stronger too....

Is the air filter assy properly on? The stock box is a pain to get just right. If it is just slightly crooked it will make vacuum sound.

Otherwise I would try a new front O2 sensor.

I could hear it with the assembly off as well. It is intermittent too not constant. W/e the sound is, is coming from the hole where the iac is but I changed the iac

mine is also doing same thing did you find out what it was?

I put in a new IAC last month. The old one was original and totally crapped out and had no idle. Had to keep my foot on the gas the whole time. When i replaced it i also cleaned out all the carbon. Now when i start it(cold) I only hear the sucking sound when i get on the gas and not at idle. It only does it for a minute or two till it warms up then it's fine. When i first got my truck i noticed the same thing. So i would say it's normal. I think the carbon build up has something to do with it.

Update:

It is still doing the same thing now after replacing it with three different brands. It just seems to be getting more noisy since when I bought the truck s few months back. You don't hear it ( as much) when at idle but anytime you push the gas puddle it sounds like a major vacuum leak. But the sound is definately coming from the iac area

If you haven't removed the TB and cleaned it thoroughly, do that next.