Hey guys,

Well, this is something thats been going on since I got my truck 50,000 miles ago. But, most have been highway, so, it hasn't bothered me...though, lately, it seems to be getting worse.

I have a 98 SS/T, so, 5.9L, and, it has true duals, 2.5" all the way out, no cats. Im not sure if that has anything to do with it but...

Truck runs great, however, when idling, it will sit there for about 5 minutes, and then, it starts loping and carrying on sounding like it has a hefty cam in it...acutally sounds cool, but, thats beside the point.
Anyway, after it does this, it starts this really loud sucking noise (vac leak?) that continues to get really loud, until either you give the truck gas, or it stalls out. It only does this sometimes, I have no idea why, but, any ideas?
Also, Im starting to hear this same sucking noise when driving...though, not nearly as loud.
thanks in advance for any help.

 

check and clean the iac,

also clean the tb if it looks dirty

start form there

 

It has something to do with the true duels. I dont know what but mine has done the same thing since I had it done. It idles fine for about a min and starts to stumble and suck air like its chocking, but not every time. I tried to figure it out to no success.

 

that sounds like it...lol
I dont know if its because the O2 is getting a false reading or what. It runs great, but, just won't idle.
But, Im kinda concerned about the vac leak I hear driving now though...since Ive been reading about the Intake leaking vac on the bottom.
Oh, and, dodgeram07....what exactly is the IAC??? Sorry, Im a newb to the acronyms for the trucks...lol
I have a Conquest, and know a bunch of those though...lol
ISC = Idle Speed Controller...is it something like that?

 

Thats it Idle Air Control. Its on the back side of the throttle body. The plenum leak wouldnt cause a problem like that. I have an M1 on mine and have the problem. I have never found someone else with this problem so it has been hard to track down. The only thing I can think is that it flows too freely and the comp cant adjust for it.

 

Well, your not alone...lol
But, I don't know...maybe a trick O2? Or, just shut off instead of letting it idle for a while...lol

Eh...no big deal, just, kinda annoying. But...if you ever figure out a way to stop it less putting stock exhaust back on it...let me know

 

I also own a 98 SS/T and this has just started recently....I have 140,000 miles on her now. It's the exact same symptoms as described above. I have a single flowmaster exhaust with cat....so I doubt that the duals are the cause. With this issue if you hit a puddle in the road or parking lot, the truck will start to idle really rough and sometimes stall out as well. This just started a few months ago and I haven't been able to figure it out. I have changed the IAC valve.....that didn't make a difference. i have also done the rotor, cap, plugs, and wires......still the same.
I also have the same sucking sound going down the road.....it's more noticeable when cold....
Other than this problem the truck runs fine.....but I don't have a clue what it is.....What is the easiest way to clean the intake......if you look down it, it is a little black.....but it always looked like this with no probs.....

 

I have to go with what Big Dodge and Dodgeram 07 is saying about the IAC. Mine was having that same problem and I replaced the IAC and it went away. I just posted a thread on how to clean the port though. The hissing or sucking sound is the IAC opening up.