I'd second the smoke test idea. I made one out of a cheap harbor freight fluid pump, a nitrile glove, and a convenience store cigar. Worked great.

I replaced my MAF as preventative maintenance due to age, so reasonable I think to try that also. Denso 1976030 from Rockauto for $65 (couple years back)

 

A little update. I got the MAF sensor in, reset adaptations and soon had both banks lean. Then eventually a CE light, so the lean codes are strong enough to break the threshold. I have not had any rich codes since like I had early on with this. So all hands point to vacuum leak. I am going to look things over and try a DIY smoke test if nothing shows up.

 

I hope this makes sense…

With the air filter box lid unscrewed all the way and the engine running, while watching live fuel trim lift the air filter lid up and see if you can make the fuel trim move high. If so, tighten the clamp nearest the MAF a smidge.

As you have pointed out in other posts, that is a leak prone area. I fought mine for a long time, even with a brand new air box/duct assembly and ultimately determined my clamp was a smidge too loose.

 

Yeah, I will look that all over. I have a feeling it might be the brake booster supply line. It was the only item I moved around a lot to get to the driver side O2 sensor from above.

 

I found a crack in the resonator. The same as long ago, but it expanded. So I sealed it up good... still getting codes after clearing them and adaptations. I sorta expected as much when I started it up and it was not a clean start, a little rough in the first half second. Will have to poke around again. Did clean the PCV and all the vacuum hoses. But I did not inspect the brake booster lines yet as I thought I found the issue. I did clean the TB again, it was not dirty tho.

 

Update:

No progress. Have not had much time to work on it, but finally dove into and I am more confused than ever. Starting to think I am having fuel issues again... need to do a pressure reading. Anyway! Today I pulled the resonator on the intake inlet and found a lot more cracks. Hard to tell if they leak so I simply removed the resonator and pulled the flexible tube tight to the filter box. Code came back as quick as ever.

So this is where I have questions. I am used to being able to block vacuum systems on engines and it having no effect on the engine itself. So I disconnected the PCV at the intake, behind the throttle body, and plugged it with a tight rubber seal. I plugged it at the intake tube also. This, in theory, isolated the PCV from the intake completely. But doing so resulted in a slightly rough idle? I then did the same to the EVAP - the singular hose that connected behind the TB with a quick release. Same... engine seemed to idle rough and things seemed worse? That should be a dead end system as far as I know - one vacuum line from engine manages it all.

Confused, I moved onto the brake booster line and finally got that dang thing off. I put new o-rings on it and inspected the engine line before installing. Looked fine. Also the check valve works, upon disconnect the booster pulled in lots of air.

Really getting frustrated with this one. No codes before coil and O2 installs. This means one of two things. I damaged something working on it or it existed before but the old O2s were not sensitive enough to pick up the leak. I have cleared codes and reset adaptations numerous times. The engine does indeed seem to lack go-power, especially at WOT. Which in itself seems odd since that is when vacuum is minimal. So that got me thinking.... a lack of fuel at WOT would, of course, explain poor performance too.

I will get a pressure reading in a couple days when I have time. I made a gauge that quick connects to the tank outlet below the passenger seat area. I was down this EXACT same road before after all. And in that case it appeared to be a fuel tank swirl basket check valve issue. Or so I suspected since swapping an ENTIRE tank from another LR3 seemed to have solved the issue. I hate to drop the tank, again, but at this point I can only *think* it is a genuine intake plenum gasket leak unrelated to any vacuum lines. Or fuel related.
https://landroverforums.com/forum/lr...advice-107774/

 

I know you know this, but don't forget that new parts can be bad out of the box these days pretty often: "No codes before coil and O2 installs"

 

Of course. But the odds of two new Denso O2 sensors being bad and 8 Delphi coils being bad without causing misfires would be an astronomical impossibility.

 

Yeah, I'd suspect the O2 sensors more if they were the upstream ones... Those could cause false lean/rich issues. Downstream ones not so much....

 

Downstream sensors can not even generate rich/lean codes anyway. They just monitor cat performance. If I have just one bank throwing a code, I would 100% consider swapping the sensor. But between throttle lag AND codes, something is up beyond a false reading. The system is actually presenting an physical issue. Otherwise I would probably ignore it all together! lol