First post - hope this is the right place... I'm a gearhead, but not that smart on the Rams, as this was to be an unmolested daily driver, and until now, has been relatively rock solid with nary an issue...

Truck is a 2002 4x2 Sport Package with the 5.9 non-Hemi (The only year this motor was installed in the Gen III's). Purchased new by me. Has 75K miles. Has always been babied as a daily driver, with very infrequent light towing duty. Has been very trouble free, save for a rear end rebuild done under warranty.

A couple of years ago, I would notice on rare occasions the idle would hunt a bit or stumble - just enough to feel - but only after the engine was warmed up, idled fine when cold. Barely enough to move the tach needle. Also about the same time the truck would "lurch" once or twice as it tries to downshift - but only under a specific set of circumstances:
- Only when fully warmed up
- only when barely accelerating from highway cruising speed, such as maintaining speed while going up a hill, or when slightly increasing speed. If the throttle is opened more than slightly (harder acceleration - it doesn't occur).
Until the last couple of months they happened randomly - just enough to be an annoyance, and not enough to even see consistent indications. And never happened when cold. Oil and fuel consumption appear to be normal - it's never burned or leaked a drop of oil in it's life.
No MIL / CELs. I've checked codes with an OBDII reader - zero.

Now the stumble is worsening, and it happens when cold. It doesn't die, feels like it wants to now. I will be driving this truck from MD to CA the minute I get this solved - so I'm a little desperate.
Just replaced air filter and PCV. Taking it in to the dealer is my biggest fear and will try almost anything first...

I'm hoping the symptoms point at a known issue by someone here. I did Search, but came up empty. I also posted this in the GEN II section as this engine is more common on those Gen trucks.
My thoughts as to possibilities:
CAT clogged. Would explain the idle, but would it cause other driveability probs that I'm not having..
MAF? O2 sensor? Please don't say plenum issues...

TIA

 

Not sure if the 5.9 has a Throttle Position Sensor, but those are a notorious problem on the 4.7 and manifests with the same symptoms. A new sensor is a $20 fix if you do it yourself, and is a simple job. Also, when was the last time you cleaned your throttle body? Gunk buildup in the throttle body can cause the plate to stick, resulting in RPM fluctuation, most noticeably at idle.

 

X2 on the Tb cleaning, and maybe some new sparkplugs, pull one out and see how she looks...

 

Probably an ignition issue...if you're on the original cap and rotor/wires/plugs i'd change them out. Cats will usually throw a p0420/0430 low efficiency code long before getting clogged...o2's the same thing but when stuck high/low or a slow switcher. Might want to check the TPS too.

EDIT: yea what the other guys said

 

A throttle body cleaning is a good idea, especially gently cleaning the Idle Air Controller (IAC). I don't remember which of the three sensors the IAC is on the throttle body it is off the top of my head, but if your getting any build up on the IAC or the throttle body where the head/tip of the IAC seats it'll be restricting the IAC's ability to to control the air flow for idle. Once your throttle blades open your engine gets enough air so it doesn't affect it then. With any luck cleaning the IAC & throttle body will solve your problem.

I just had a very similar problem with my car and with a cleaning it runs WAY better. My car was to the point of actually stalling once in a while during idle and now it's all but gone.


From: Dodge ram FAQ in the 2nd gen section

 

Update:

After reading up quite a bit, I decided to replace the TPS and ICV - hoping for quick and cheap solution... The TPS is very easy to access so I did that first. Problem remained.
Next was the ICV. Harder to get to but not too bad. Seemed to help but the problem was still there.
With a coast to coast drive a few days away and out of time, I did the unthinkable - I took it to Pep Boys. I told them to only replace the Dist cap, rotor, plugs and plug wires . Mine were all original with 75K miles. They recommended a a fuel inj cleaning (total BS) and I figured what the hell...
Problem solved.
The cap and rotor were badly pitted and I'm sure that was the biggest culprit. The mechanic - actually a really good guy - said the wires were in bad shape as well.
I went ahead and had the pre-cat O2 sensor replaced at the same time for piece of mind.

Just arrived in CA after a 2800 mile drive pulling a heavy U-haul. Ran great.
Hope this helps.

Mitch