So the truck picked up a new trick lately. The idle (in park and stopped in drive) is noticeably rough. Not lumpy or throwing any codes but a low vibration. It does not do this when in neutral, idling in neutral is smooth as silk. Also when driving it accelerates and runs smooth

Tried the usual suspects, new MAF, new upstream and downstream o2 sensors (they were due anyways), cleaned the TB, no visible cracks in the intake tubing and reset adaptions. Also plugs are only a few months old and the injector pulse rates are all the same

Any thoughts on the source? drying coil maybe or battery maybe? I checked the the battery voltage when not running is down to 11.7. Weirdly noticed too the live value for my fuel rail pressure sensor is 0v, not sure if thats a clue either.

 

Your battery is likely dead if that's really the voltage with all systems off - I'd disconnect it to be sure before replacing the battery.
The fuel rail pressure sensor voltage being 0v is interesting - but I'm pretty sure there is no fuel pressure sensor in the 4.4.
Any misfires detected?

 

It's kind of a long shot, but easy to check. Try pressing the "Econ" button on your climate control to see if it goes away. This will force the A/C compressor to its lowest output. If it changes, you may have found the source of vibration. I'm perplexed about "Park" being rough and "Neutral" being smooth. Any chance releasing the brake while in neutral causes the same rough condition?

 

Following up in case this pops up in someone's search down the line.

I didn't replace anything that didn't need it anyways, but this one comes down to a K.I.S.S. situation.

Paid attention to whether the pedals affected it like @P-Bod mentioned, and sure enough the vibration was there when sitting still and the brake pressed, but went away when releasing the brake (in drive). Looked at the brake pads and they were getting low. Replaced the pads and voila, no more vibration. Guessing they must've worn unevenly or were a low quality pad

 

Glad you got it fixed! I was thinking more along the lines of the brake booster possibly having a leak and somehow affecting your idle. I don't know how pads could make the difference, but fixed is fixed!