I have a 98 dodge ram 1500 4x4 with the 5.9l 360 in it if i start it up and let it idle it will sound like theres a vaccum leak around the throttle body but after a minute or two it will start to idle rough like it wants to bog down and the noise will turn into a LOUD sucking noise its coming from the IAC valve ive tried everything i can thing of swapped multiple IACs replaced tps and map cleaned throttle body a few times then pulled it out and cleaned it out good still nothing no codes pop up on it also any help would be appreciated

 

Unplug the front O2 sensor, and start the engine up from stone cold. See if the problem goes away.

 

I had that happen couple years ago and it was the O2 sensor going. Get NTK from rockauto only.

 

Both o2 sensors are relitivley new but I gave it a try any ways and here's what I got the hissing noise was still there upon crank but at the normal volume not insanely loud just a nice quiet idle it never started to bog down or hiss/such air loud but I got to spraying around the intake manifold and the motor revved up ever so slightly when I sprayed around back of the ac compressor. But no matter how much I sprayed it never changed again...wondering if I've got an intake manifold gasket leaking as well....

 

could try re-torquing the intake bolts.... see if they are loose. Might fix it. Or, might tell you you need to re-seal it.

 

If you have access or know someone that has a smoke machine, I would try that. Maybe you have multiple leaks.

 

[QUOTE=Austin25;3265586]I have a 98 dodge ram 1500 4x4 with the 5.9l 360 in it if i start it up and let it idle it will sound like theres a vaccum leak around the throttle body but after a minute or two it will start to idle rough like it wants to bog down and the noise will turn into a LOUD sucking noise its coming from the IAC valve ive tried everything i can thing of swapped multiple IACs replaced tps and map cleaned throttle body a few times then pulled it out and cleaned it out good still nothing no codes pop up on it also any help would be appreciated[/

I had the same problem. After reading some other forums I found that unplugging my upstream o2 sensor stopped my truck from doing this. Truck gets bad gas mileage with upplugged and gives a check engine light but at least no crazy surge of air sucking and engine about to die. Waiting on upstream o2 sensor now. I also read to go with NTK sensor because it’s OEM. Hope this helps someone.

 

Did you look at the vacuum hose on the front of the throttle body. If you trace it it goes to a sensor on the back of the engine that sits on a rail "sorry don't know what the senor is called". When I was performing my TC change this past week, I noticed that when I removed that vacumm hose, it was cracked along the bottom. Just a thought.

 

Hmm that’s interesting my 01 has a sucking when I first start it then it runs rough starts to bog down and sucking gets really loud but then it revs up for a second all on its own and all is normal. Sometimes it will do it 2-3 times if it’s cold or rainy out. It’s been doing it for years and I just never gave it a second thought for the longest time. I changed my cap and rotor awhile back because I was having really hard starts when it rained and it doesn’t really do it anymore. When it does do it it’s nothing like it used to very mild. Wonder if it’s the same thing as your truck. Be sure to post your findings if you figure it out.


EDIT HOLY MOLDY THREAD PEOPLE 2015!!!!!

 

Mine did the same thing as yours for about six months. Every time I start it after about a min and a half it sucks air idles rough for about 45 seconds and then clears up and runs great. I finally replaced the O2 sensor the other day. Mine has finally quit sucking all the air and bogging down. Been 2 days now with new o2 sensor and all is good finally. Before you start your truck unplug your upstream o2 sensor and see if it still does it. Fixed mine. If it works for you make sure to get a NTK o2 sensor.

update:!! new upstream o2 sensor fixed the problem and yes the plug is kinda hard to get to. I have long arms so I bear hugged up around the transmission and got it I clipped.