Now to start off i just want to say my RPMs do not fluctuate when the car is running, it is consistent. I’ve had my 01 3.9 dakota for about 2 years and can not figure out the idle, the truck shakes like a bitch. I’ve done proper tune ups, didn’t cheap out on anything. regular oil changes, changed every vacuum line, cleaned and changed IAC valve, new air filter etc. I cannot figure out why the truck shakes with everything seemingly in good condition, i’m hoping it’s nothing internal. Just let me know ur best ideas of what it could be, thanks

 

Possible bad harmonic balancer and/or bad engine mounts.

 

Either of the above, hard to say which. The 3.9 is neutral balance so i would doubt the balancer.

 

the 3.9 is an "odd fire" engine, like the old Buick v6s,, they will never be totally smooth, though it seems some are worse than others. Possible vacuum leak? maybe plenum leaking?

 

wrong. while the block is in fact a 90 degree V6, the crankshaft is cut with offset journals to convert it to an even-firing V6 on 60 degree centers.

 

no, I am NOT wrong. apparently you don't know what makes an even fire an even fire, and an odd fire an odd fire.
it has nothing to do with being a 90* V6. That is the angle between the left and right bank of cylinders, has NOTHING to do with the gap of firing between the cylinders!!! 60* V6s come in both odd fire and even fire versions too.
An "even fire" V6 fires a cylinder every 120* of crank rotation. (remember; 4 cycle/ a 2 cycle would be every 60*) ALL inline 6s are like this as well. even fire.
An ODD fire engine has differing gaps between number of degrees between one cylinder firing and the next. Look in the factory service manual!!! Ignition section, front page of section right under the section index. It will say that one cylinder fires 112* after the previous one, the next cylinder fires 128* of crank rotation after that one. next cylinder fires at 112* after that, then 128* again.
an odd fire engine will never be as smooth running as an even fire.

 

A few tests would be good. While idling, carefully pull each plug wire one by one and see if anything changes. If you pull a plug and nothing changes, you have a problem with that cylinder.

Next would be to rent a pressure tester, check all your cylinder pressures. If one is low, it may cause roughness at idle as the pressure is escaping before it burns.

You said you've done well with maintenance and tune ups, but have you replaced the cam and crank sensors? The cam sensor under the dist can sometimes rust or carbon up and cause issues. The crank sensor in the bellhousing when it gets lazy is well known to cause all sorts of oddness. From bad idle, random stalling, misfire, and eventually no fire no start. I'd pull these from a junkyard and change them for a test, do not get 3rd party on the crank sensor. You can pull them from any 3.9, 5.2, or 5.9. these two sensors are the same on all three engines.

Also, while yes the 3.9 is technically an odd fire, it's not like an old buick V6. The old Buick V6 shared 3 crank pins until they changed it later. Dodge decided to use split pins to smooth it out rather well, it's only 8 degrees from full even fire. This is stark contrast from 90/150 so it should not have major shaking like an old buick fireball.