I have been stalking for a little bit and thought I would chime in. The thread on land rover world is mine.

my idle bogs when coming to a stop, and sometimes after a warm start. But, it does not fluctuate rhythmically between two rpm points. My DSM days tell me that is idle surge caused by a dirty/defunct idle stepper motor. Unlike the early 90s ride, this motor is integrated into the throttle body and cannot be replaced separately.

I know we cannot do it with the GAP tool, but I would be surprised if you could not test and set the idle via SDD. At the very least, I would reset throttle adaptations and see what that accomplishes. (If you already did, I apologize. I did not reread the earlier posts; only the updates).

Also, if I remember correctly, after replacing the fuel purge solenoid once, it is supposed to click. That is the valve "purging" the fuel vapors into the intake system.

since, like me, you have had this thing apart--and I am mind mapping with you--it is possible that a leak was created on the back of the supercharger. If memory serves, there is the intake manifold vacuum line and the MAP sensor connected to the driver Side intake manifold. Either of which could create a beautiful vacuum/boost leak.

I'll update both of you this weekend (here and on land rover world) on the results of the in tank fuel pump replacement and DMTL troubleshooting.

 

The rhythmic fluctuation does not happen every day but the bog down is daily. Don't know if I mentioned it, but there are times when the engine runs as smooth as can be regardless of load, in idle and at all times while underway or higher rpms when stationary, there is no shake, shudder or vibration. But reading your posts it does appear we have a similar issue.

I see you've already replaced MAF sensors and PCV with no impact.

Does your fuel filler neck, with cap removed, make a rumbling noise with the engine running?

How much oil & gasoline drip from your part load breather?

 

Mine is the same: Smooth while cruising and at higher rpm idle. For clarity, I did not replace the PCV valve diaphragm. I only put new o-rings on the pipes to eliminate any possible vacuum leaks from those areas. I replaced the diaphragm on our other lr4, but ended up having to replace the whole valve cover. In that regards, it did throw a code.

I did have a massive misfire that caused me to change the injectors, plugs, and ignition coils. I also did all of the intake gaskets and supercharger snout and coupler.

also, I am not sure which breather you are talking about. I'm sure I do not know the proper name for them. I will say that while mine had a little oil, there was no gasoline present and there was only a very small quantity of oil.

there are only a couple of days that gasoline can enter the crankcase. It seems like you ruled out the majority. I would suspect that something is happening with the tank to purge valve connection, allowing fuel to enter. I have all of the parts necessary to drop the tank this weekend. I will let you know how the test drive goes. I know this is super frustrating and am sure we can figure it out together.

 

The part load breather is connected to the top of the throttle body and the right side PCV, the full load breather is on the left side and is connected to the intake plenum. My full load is always dry, free of fluid or smell but the part load breather is always dripping very dark oil and gasoline. Now the main dealer has had the super charger off 3 times in the last 2 years and has always insisted everything looks normal and in spec. The last time a few months ago I took the opportunity to inspect the pulley coupler and it was fine, but the inside of the supercharger was a mess with oil residue and the intake manifold and valves were coated in thick carbon deposits despite my frequent use of PEA via the part load breather.

 

Gotcha. No, my part load breather has a tiny bit of oil, but no gasoline. I can understand the oil in yours (If the internal baffling and what not that makes up the PCV system is clogged), but not the gas.

the crankcase dilution is the symptom. Like one of the previous posts, it is possible that the piston seal within one of the HPFPs is leaking fuel into the crankcase. I just find it unlikely--especially given the fuel pressure = commanded pressure. Another way is through a cylinder. A leaking injector / increased fuel can bypass the rings and leak into the crankcase. However, some sensor (map, maf, O2) is calling for more fuel.

if that is not the case, then I think we are looking back at the fuel purge solenoid. Somehow, the fuel vapor is saturated enough to cause a rich reading by the lamda o2 sensors and simultaneously fouling the oil in the example above.

oil in the supercharger is normal. I had the same concern and posted a picture in the other forum. The other gurus stated that theirs looked the same. Likewise, direct injection is always going to cause carbon buildup on the intake valves, as the gasoline isn't there to "wash" them.

I missed your other question from the last post. I have never opened the gas cap while running, but I will play with that tomorrow as well and let you know.

 

There are a lot of things that can go wrong pulling it that many times. Did they replace the intercooler and intake manifold gaskets each time? Did they forget to reattach a sensor wire or not seat a vacuum line all the way? Did they foul the MAP sensor o-ring creating a leak?

humor me and warm the car up, turn the heat on high temp, high fan (including rear climate control) and see if the idle shaking goes away while driving.

if it works for you, I'll tell you my thoughts

 

Just to give some other points of reference, on my car (which is running pretty much as normal - a little high on fuel trims, but not too bad - no rough/surging idle), I have always had some oil in the part load breather, but never any gas odor. I also opened the gas cap while it was running, and I don’t hear any noise down in there. Regarding the purge valve, I don’t think its supposed to be open when the car is idling - only when your moving and when other specific conditions are present. I put a stethoscope to my purge valve tonight while it was idling for a while and I don’t hear any noise coming from it. So, if you’re hearing that valve clicking while your at idle, that might be one problem.

You mentioned your o2 sensor fluctuating 0.1v-0.9v while surging, and 0.9v otherwise. My o2 sensors fluctuate between about 0.2v-0.7v in an even pattern - just kind of back and forth like a rolling wave. It’s my understanding that’s what it is supposed to do as the engine maintains the fuel mixture, but not 100% sure on that.

I’ve got my GAP tool up and running again, so if you guys want me to run any values for comparison, just let me know.

 

@jlglr4 you are right; the voltage should fluctuate on the narrow band o2 sensors. We have two lambda sensors (wideband) in the exhaust manifold. The lambda sensors inform the pcm as to the af ratio after combustion. I would assume that the narrow band o2 sensors after the exhaust manifold, but before the cats, measures whether there is a leak in the system prior ...or further validates the reading of the wideband.

the narrow band will display open loop mo' better (If I remember right) and that is the fluctuation you see going from slightly rich to slightly lean as the computer adjusts for that perfect stoiciometric ratio.

I am still working underneath the ride. More thoughts tonight

 

Quick update. In tank fuel pump and filter install went well and may have solved the problem (knock on wood). I finished the work on Saturday and did a short drive to the gas station on Sunday. LTFTs were high (~10%), but STFTs we low (~ -4.5%). O2 sensors read well. However, coolant temp sensor #2 read 11C while #1 read 47C.

I am attributing the mismatched coolant readings to not being warmed up. I am reasonably sure that the #2 coolant sensor would heat up once the thermostat opens.

Anyway. Monday's drive to work showed a little bogging when coming to red lights, but, driving home, it was not present. Likewise, on this morning's drive, there was no idle bogging.

I cannot rule out environmental factors though. It's been warmer the last few days... I'm going to keep an eye on it this week and report back.

 

I've an update as well, though this may well be a red herring, however after over a week of monitoring variables, I've noticed the rhythmic idle drop appears to be consistently induced by removing and replacing the gas cap and takes about 20 minutes to right itself. It does not however have any impact on the other random idle drops etc. And again on some drives I can load it up and idle stays high and smooth and other times idle just keeps dropping and shuddering. Also noticed and perhaps this is normal but with just a quarter tank of fuel, the gas cap is very wet with gasoline and that strange rumbling/chuffing noise from the filler tube.