I wonder if liquid fuel somehow got into the vapor canister. The think the liquid fuel can degrade the charcoal in the canister, which might account for that sludge. The sludge could also be preventing the purge valve from closing completely. The rumbling could be the engine vacuum pulling air through the liquid-filled canister. It would also explain the rich fuel mixture.

 

It's behind the spare, above the rear diff. Regardless, it is hard to make sense of this.


Above, I circled in green where I think the purge valve from the engine bay connects (I have never traced it).

if the noise is in both the filler neck and the engine bay purge valve, it HAS to be something with the EVAP canister / DMTL pump (4 and 5 in the diagram)

below is what the connections look like. The white piece with the electrical connector is the DMTL pump.


below are the two connections from the gas tank to the evap canister. Blue port on the tank in the background is where the filler neck connects



finally, here are the front fuel feed lines on the front of the tank.



as you can see, the fuel purge valve in the engine bay does not connect to the tank.

I think the next step is checking the connections and function of the evap canister components.

 

beat me to it. May have to pull the whole charcoal canister..

 

But, as always, you’re response is fully illustrated. Very nice.

I think the purge valve/line connects to the canister (purge canister outlet), then the canister connects to the fuel filler tube (purge canister inlet). The canister or DMTL also should have a fresh air connection that is open when the canister is actually purging, and is closed otherwise. I imagine this arrangement is supposed to keep the fuel out of the canister since the caniser inlet is connected far up and away from the level of fuel in the tank. But if the tank is overfilled or somehow becomes compressed, the fuel level can perhaps make it up to the inlet connection, and when the purge valve opens, it sucks fuel down into the canister instead of vapor.

If this is the problem, it’s a mystery how there are no fault codes.

 

No likely, I've never overfilled or had issues with filling.

 

Looking at the blow up of the filler neck, there are three lines: red, green, and yellow. Red terminates at the fuel filter on the top of the tank (large connection to the right of the electrical connection below)

That breather, underneath the fuel filter, connects to another line. I'm assuming to allow contraction and expansion of gas in the tank and equalize appropriately. I circled the nipple in green on there the in-tank line connects.



the green and yellow lines come from the evap canister. One, I assume, is the fresh air intake to purge the fuel from the evap canister. If this is clogged, that could create issues by itself. Possibly, creating vacuum that sucks the fuel through the system, from the tank.

you may want to pull the right rear wheel well splash shield and inspect those three lines as they connect to the filler neck. If I remember right, there is also an in-line air/fluid separator, designated as #2 In the earlier diagram.

 

Nothing much new, just a few more observations:

The gurgling and chuffing occurs when the purge valve is ticking regardless of a 1/4 tank or a full tank.

I disconnected the purge valve from the input side which eliminated the filler neck noises as well as the ticking from the purge valve but this had absolutely no impact on whether the RPM stayed consistent, fluctuated or dropped too low.

And to reiterate RPM observations: Normal smooth idle rpm seems to be at 630 though frequently it sits at 700-900 rpm and frequently sits 1200 rpm REGARDLESS of whether A/C, heated seats, heated windscreen, etc are on or off ALTHOUGH 1200 rpm idle is NOT as smooth as 630-900 rpm. What is also consistent is when the shuddering occurs - ONLY when rpm drops to 500 to 600 RPM, with or with out load though adding more loads drops rpm lower and lower additively AND sometimes the reverse happens - adding more loads causes rpm to increase from 630 up to 700 rpm - obviously without shuddering as the shuddering ONLY occurs when below 600 rpm AND sometimes turning off loads causes rpm to drop as low as 500 rpm.

Also a new unrelated observation: sometimes during hard acceleration with windows open I hear a noise from the undercarriage like rattling screws in a glass jar AND sometimes when stopped in drive and then initial accelerating I hear a metallic knock/clunk from the drive line (NOT suspension).

I am at the point now where the severe lack of support and skill from the main dealers as well as what I have observed as a massive decline in product quality from JLR, after 10 JLR vehicles in an 18 year period, the amount of money spent in recent repairs and the value (or lack of) placed on trade for this truck, I am now exploring other brand options and letting this one rot away....

 

Really sorry to hear this. Those rattling noises are likely the catalytic converter having failed from the rich mixture persisting for too long. That’s probably what is causing your idle issues as well. The catalyst supports melt (clogging air flow - idle issues) and collapse (causing the rattle inside the converter housing).

But there seems to be a story here that addresses all the issues - failed charcoal canister putting soot into the purge valve, which then sticks open putting an extremely rich mixture into to the engine (and some gas in the oil), which takes out the catalytic converters leading to your idle issues. I don’t know what the cost would be, but a couple new converters and new charcoal cannister, and you might be good to go with this truck. I’d check out a few other things first (compression, oil sample for metals, and, pull the pan to look for charcoal grit or metal shavings) - just to make sure its otherwise sound and that charcoal didn’t get down into the engine. But it might be better than giving up on it. Just a thought.

Again - sorry for your troubles, and hope things start looking up.

 

One other thing - remember that there are warranties other than your new car warranty that might help in some instances, particularly with respect to emissions equipment (all of this stuff we’re talking about is emissions equipment). There’s a Federal Emissions Warranty that covers some parts for 8 years/80,0000 miles, and I’ll bet the state of New York has some kind of protection on emissions equipment as well. I have no idea if it will help in this particular case, and you might need to jump through some hoops (like maybe failing an emissions test), but could be worth looking into.

Good luck.

 

But if I've removed the purge valve from the equation by disconnecting it from the vacuum lines and the erratic idle persists, would that eliminate the charcoal canister as well?