Well PCV Valve seems to have fixed the problem in my case, or at least I think that's all it was. While I had the air breather off I changed the air filter and cleaned the throttle body butterflies. Seems to idle ALOT better on cold start up, then after a few minutes I notice a bit of a hiccup once in awhile... I'm happy tho, I can live with that!

Buffalo, hope you figure yours out. Maybe you got a bum PCV valve?

 

Mine does that for about 30 seconds to a minute on a cold start in hot or cold weather, has since I got the truck at 74,000 miles and it has about 130,000 miles on it now. Mine will sit around 900-1000 rpms and bobble down to about 700-800 and hiss through the throttle body for a couple seconds then jump back up to 900-1000 rpms.

I've replaced the IAC, TPS and PCV a couple times, the CMP, upstream O2 sensor, The plenum gasket then replaced the intake with an airgap a few thousand miles later and the vacuum line check valves but mine still does it.
I didn't replace all that trying to get rid of the problem but I have noticed that none of that changed it. I can't remember if the PCV ever affected it at all.

 

well PCV didn't fix it after all. Now that I look at it closer, it does have a white vapour like exhaust for the first few minutes when it's sputtering and idling rough. I thought this was just water vapour from condensation in the morning...

Once the idle smooths out the vapour seems to go away... I don't smell AF in the exhaust though, just up front by the engine.

Buffalo Rich, are you seeing the same thing? Maybe we're looking at a headgasket?

 

lol thats what i was thinking

 

This seems like another common dodge problem. Are all of ya'll's motors 5.9's or 5.2L? It doesn't matter on mine whether it's summer or winter, just the same hiccup on cold idle.

 

I payed attention to it yesterday and I lied, it doesn't do the hissing noise anymore but it does bobble like it has a slight misfire, but after it runs for a minute it runs great.

 

evap purge on pass fender.system test on start up leaks fuel vapors into the tb.

 

Think I may have found the problem (or maybe just another one). I've noticed a AF smell at the front of the truck since I got it, but not a whole lot of white smoke at the tailpipe, just some white vapor that disipates after a couple minutes once the truck warms up. Looking closer at the front of the intake there appears to be some AF stains/crusty buildup. This is also where the tstat housing is though, so it could be that.

Its likely that the AF smell is AF seeping out and evaporating on the heat of the engine, as I don't see any leaks under the truck or at the waterpump or heads. I'm wondering if it's possible that this is the cause of the rough idle at cold startup though? Is there a water jacket in the intake manifold on these trucks that would cause the AF to leak into the combustion system, or is this more likely just a leak tstat housing?

 

I'm not seeing any type of fluid leaks (AF or otherwise) nor do I see any odd smoke. Once I start the engine it acts like it's mis-firing, then it kinda chokes down to a couple hundred RPM's (all the while sucking through the intake) then just when I think it's gonna stall it catches itself and fires back up to normal idle speed and runs fine from that point on until the next re-start. If I try to drive it from a cold start/re-start, it chugs and acts like it mis-firing an wants to stall. It doesn't seem like it could be a vacuum leak since it only has this problem on start up not all the time. Very interesting to keep hearing that more and more people are chiming in with similar probs though.

 

I have been trying to solve this exact problem for about a year now. I have pretty much tried everything. No codes show up, even while it's doing it. I can't tell you how many old threads I've read that talk about the same thing. One guy even has a video of his doing it. I'll try to find it and post it here. I seen this is an active thread so I registered just to reply and keep it going until we find an answer.