Ok, this is going to be a long explanation. I replaced the motor 1000 miles ago. The odometer has 135,000 on it. After replacing the motor, it had a slight miss at idle. I have had the injectors cleaned and flow checked. I removed the Airtex fuel pump and installed a delphi. The intake has the Hughes plenum repair. The crank position sensor is new and from the dealer. New idle air motor,from the dealer. New map sensor,from the dealer. No codes. The long term fuel trim was high, at 20. To much air and not enough fuel. Well after doing all this the long term fuel trim has come down to 5. Better for sure. Front upstream and down stream o2 sensors have been replaced with NTK which is made by NGK. The truck still idles rough and only intermittent. Not all the time. You would think if it was the computer, which is a reprogrammed unit from a place here that all the "Jobbers" use, it would do it all the time. New coil, accel. Plug wires re-run per the TSB "Spark Knock". I am wondering if it could be the cam shaft position sensor, or the manifold air temperature sensor. I have read that the cam sensor can cause rough idle problems intermittently. Really frustrating. I am pretty sure I do not have a vacuum leak. One other thing, this motor has been rebuilt three times. Longer story and do not even want to go there. Anyway,everytime you re-surface the heads you loose a little in head height. I am wondering if where the intak manifold bolts down, the ends front and rear are hitting the block, and not allowing the mainfold to seat properly on the heads. Which is causing a vacuum leak around the mating surface from the heads to the intake. Can't tell you what it has for vacuum, but can buy a gauge and put it on and let you all know. Would be tomorrow at the earliest. It is a 5.9 360. Cat is also clean, not stopped up at all. I have replacement fuel injector pigtails which I plan on putting on since the old oem ones just kind of sit on top of the injectors, some better than others. Long one huh? Thanks Mike.

 

I'm no engine guru, but I've been consuming alot lately, yet still take this with a grain of salt and just throwing stuff out for consideration into the equation here.

1. Did you have fuel sync set? I'm not sure if that was meant by the fuel trim @ 5. I'm under the impression that this should be set with a snap-on mt2500 tool or done by the dealer.


2. I was going to refer to wire TSB, but you got that.

3. Crank Position Sensor sounds like a good check, assuming you've ruled out other things, seems you have.

4. I can't recall what ppl suggested here to spray around gasket interfaces to check for vacuum leaks. That would be a good check on your last mention there.

 

Clean the AIC (I think thats it), anyway, the sensor on the backside of the throttle body. See if that helps.
To check for the vac. leak at the manifold, spray some carb cleaner there, if its sucking air it will suck the cleaner in, it should raise the idle when your spraying it, if its leaking.

 

^word.

https://dodgeforum.com/forum/dodge-r...n-the-iac.html

 

Fuel sync was set using a snap on scanner. Idle air motor is NEW, and passage is spotless. Crank position sensor is NEW. And as far as vacuum leaks I did not mention that I probably have the cleanest intake in town from all the carb cleaner I have sprayed around the intake looking for the leak. Thanks though. Anyone else with ideas. I am welcome to anything. Keep em coming. I am not giving up until this is figured out.

 

Good deal.

Any consideration of replacing back some original sensors/parts, the easy ones, to see if any change. Again, just a thought here, but sometimes changing too many things at one time or near eachother increases the fault tree.

I'm done being able to offer any ideas but will be watching and learning. Good luck, but I know there are smarter ppl here.

 

If you suspect the intake may not be sealing to the heads properly.... Disable the PCV system. (plug both sides....) Cap off all vacuum ports on the intake. (don't drive like this.....) Take off the oil fill cap...... Start the engine. You should feel a breeze blowing OUT of the hole, if you have vacuum there, you have an internal leak somewhere.

Heads have been resurfaced three times??? Are you using the rubber seals at the front/back of the intake?

 

Heads have been done three times. This motor has been gone thru three times. First was at machine shop when the first oem motor cratered due to plenum. Second time was because of bearing failure and this time because the last idiot did not install the oil pickup tube right and caused thrust bearing failure. And yes I am using rubber seals on the ends. And thanks, I will try what you said. Will post back tomorrow.

 

Just a thought, did you reset the ecu after changing the sensors?

 

Since the intake manifold seal is suspect: Did you perform the vacuum test? And catch it while it was running roughly? If so, what's your elevation and what were the results?

When I have a strong suspicion about something like that and ignore it, I always regret it. Even if I find a problem elsewhere I can't shake that nagging little voice in my head telling me that the thing I suspect is going to wait until it can do a very dramatic Murphy's Law failure.