3.9 vacuum leak?
 

Ok, I've tried and tested everything,and can't find what appears to be a vacuum leak in the manifold. I plugged off all vac lines from the manifold and TB. Still rough idling. I ran the crankcase pressure test too. I get positive pressure and no oil pooling in the plenium. Ideas? Suggestions? Anyone else run into this situation before?

What is manifold vacuum at idle?

Hey You, it's the Dakota guy you've been assisting me with. Thanks for your help! Much appreciated! Anyway, it's 19 in Hg pulled from the plenium port, and the MAP reading is 5 psi

Hey You, it's the Dakota guy you've been assisting me with. Thanks for your help! Much appreciated! Anyway, it's 19 in Hg pulled from the plenium port, and the MAP reading is 5 psi.

It's also smelling rich when cold ( open loop)

That's actually quite close to where it should be. The map reading seems a little off though..... (by about 50%) is the little rubber elbow from the throttle body to the map damaged?

No. It seals fine. The symptoms don't go away, even when cold if I remove every single vacuum line coming off the intake stack, and plug the ports off, including the MAP sensor.

What are your symptoms?

rough/shakey idle at all temps and rich when cold. (idle warmed up is about 670 RPM. It holds idle well and same 670 in gear, or not, and with A/C on or off.)
Cold idle is about 900 RPM

Is there a way to test the accuracy of the MAP sensor?

Compare the reading you are getting from the vacuum gauge, do some math, (convert in/hg to psi, or whatever measurement the PCM reports) and see if they are even close.....

How old are your tune up parts? What plugs ya got in there? Are the wires routed per the TSB?

the vacuum guage reads 19 inHg
30 (STP) -19 (running) =11 (actual pressure)
5psi -MAP reading while running
5psi= 10inHg
So 10 InHg is close to the same reading
I think the sensor is reading ok, I don't know if the pressure is correct.
Also, while driving and at idle, the timing advance reading from the scanner is all over the place. As I accelerate, the advance drops to 14*, as I decelerate, it jumps to 40*....at cruise or idle, it will start to wander. ( i can't read the timing mark on the crank dampener while it's running, but the strobe of the timing light shows a steady no wander situation against a stain on the dampener...and advances as it should) I can't compare a "proper" running truck to this one because I have never driven one before. It seems to cruise and accelerate smooth, with low end torque strong, but seems to lack horsepower. Still nothing to compare to.
Idle seems a bit low too.
I have changed out too many "obvious" things. never changes the symptoms. Only improvement was taking the o-ring out of the TPS which stopped the surging idle.

I'm starting to think the ECU (PCU) is the culprit. Possible a bad ground or short? The timing readings seem to be benign.

As for the tuneup parts, I changed out the cap, rotor, wires, plugs, o2 sensors, IAC, cleaned TB, replaced injectors, replaced CAT,
Nothing changed the performance, except the injector replacement added 100 rpm to idle and the o-ring I mentioned binding on the TPS

What brand O2 sensors?

The 3.9 was never a powerhouse to begin with. :D 2 or 4 wheel drive?

Could try resetting the computer, just disconnect the battery, turn the headlights on, count to ten, turn headlights off, hook battery back up, turn ignition to "on" (not start), count to ten, THEN start the engine, drive it like you stole it for 15 minutes or so, and see if it feels any better.

Denso sensors from rockauto.2wd

Good enough.

Give the pcm reset thing a shot, see if it behaves any better.

ok thanks