Hello Gents...and not so Gents,
I am hoping someone found the magical answer, I can't be the only one who has lost sleep over this.....a case of beer or your choice of spirits to the lucky winner, ( I'm not kidding, I will send it to you ). I have been chasing the miss at idle / off idle stumble for a few months, running out of ideas. Here is the scoop, I bought this 99 5.9 with pph headers high flow cat and flowmaster. The previous owner also did the Hughes plenum kit (looks dry in there),It has a 50mm fastman ( which I have replaced with stock until I find problem). This is what I have done looking for the culprit.
new cam sensor
dist cap (brass contacts)
rotor
Mopar wires ( TSB reroute )
Irridium plugs
crank sensor
coolant temp sensor
TPS
IAC
MAP
removed fastman and replaced with clean stock (soda blasted and ultra-sonic) throttle body
accel coil
catlytic conv.
air filter
bosch injectors
upstream O2
Evap solenoid valve
PCM
I think that is all the new parts. I have checked the fuel pump psi and it runs 48psi, sitting in driveway, I still may replace it because it doesn't tell me volume so maybe while driving it drops psi or volume.
Here is what it does...as if you don't know.... start it you can hear a small miss at idle, when in gear at stop it stumbles/misses, when you accelerate it stumbles off the line, just off idle. seems to run ok once moving.
Now I will say, I started looking for this when I got a flashing CEL under load, I took it home, code showed a #1 miss fire, Plug had burned the platinum tip off.That is when I started throwing money at it like an 18 year old behind the peep show glass. Now I have not stood on it to see if flashing comes back after the cat was replaced (last thing done). I also need to replace the header gasket at head on drivers side. It does have a leak, dont know if it is enough to cause the CEL, but it is on same side as failed plug, and it may leak enough to throw off O2, not sure how big a leak that would take, you can hear leak, but does quiet down when warmed up.
The only things I have left is the fuel pump and removing intake to check physically for plenum leak. If I pull the intake I have a Hughes air-gap that will go on.
Please take mercy on my debit card.....it is cutting into my alcohol and jeep budget.....(yes, I am not married) any help is appreciated and the winner will be rewarded.....no joke....
Thank you

 

In this order:

1. Get rid of the iridium plugs. Just standard copper plugs, manufacturer of your choice. These motors don't like 'em.
2. Crank sensor? Is it a mopar sensor? If not, get one, replace it.
3. O2 sensor. What brand? Is it bosch? If so, replace it. Denso, or NTK please. (NTK are OEM.)

 

Thank you, I have autolite copper core to go in, I have 3923 and 5224, ( like I said ,I'm not married, no body to say "no" ). I will toss the bosch o2, and I will stop at dodge on way home and get a crank sensor, hell I'll get the o2 while I'm there.
You are the first so you have a good chance of getting the prize if this works.....I'm not bull sh**ing about this....it's worth every penny to me to figure this out.

 

Do the parts one stage at a time, see what makes the biggest difference. I suspect you will need all three in any event....... These trucks are just picky about some parts.

 

I have listened to the wise words on the wind. I have a Mopar crank sensor ( I put a NAPA in that will come out, I have pph headers and it makes it pretty easy), copper core plugs, I have a NTK o2 sensor on the way (the bosch I will keep for my 96, 5.2, 1500, it doesn't seem to care what I put in it, it's had a bosch for 6-8 years now) , and even though it is discontinued, (makes it a personal challenge then) I found a dealership in california who had one and only one, original Mopar cam position sensor so I figured why not......
Thanks for the help......these magnums are a different animal from the B , RB and LA blocks of my glory years.....I'm learning.....slowly

 

Never have I met a motor that is more picky about it's sensors than the magnums.......

 

OK, I have replaced the leaking header gasket on driver side. I also replaced the intake air charge temp sensor just for fun. I have the new Mopar brand crank sensor in as well. Tonight I will replace the header on passenger side, get the 3923 plugs in it. I don't have the o2 sensor yet, or the cam position sensor, they both should be delivered tomorrow. I think since I have the wheel off on pass. side I will go ahead and replace the rotors, I have them, may as well use this time to put them on, (one rotor has a light shutter, even visible on rotor). Don't know if I will get to try it tonight or not, I will keep you posted.

 

Ok, I removed the bosch o2 sensor I had put in, removed the irridium plugs and the echlin crank sensor.....I replaced the plugs with 3923 copper core, the o2 and the crank sensor with Mopar. while I was at it I installed a new cat. and a new manifold air charge sensor. when I first started it it sounded ok idling so I backed down the driveway...all good, but then when I started down the road it would not rev, I thought "what the h**l did I forget to hook-up? I turned around, back up driveway, got out, found nothing, reved it a couple times and tried it again....it has never run better. My thought is the pcm had to set itself to the new sensors even though I had done the "remove ground and turn key thing" I really don't think that works....on my jeep you drain the brain by touching the ground cable to the positive. Non the less, the bottom line is it runs, and never better. On a side note....before the injectors where put in, I averaged about 18, maybe 19mpg on freeway. Now with new injectors and running good I average 22 to 24.
SO....HeyYou.....name your drink of choice, and a place to send it....you win, it will be my pleasure.

 

I had that once, did some work and it ran poorly for neighborhood mile test, had to use the throttle to keep from stalling. I too did nothing, just kept driving another mile internally scratching my head to figure it out. It smoothed out on it's own a mile or two later and has been fine since. That was two years ago.

 

Excellent.

Not concerned about the drinks though. I don't generally do alcohol. (I may drink two or three beers in a year. When I was in the service though, totally different story. )

Drive it, and have fun.