Yes!

Thanks for following up, so it was hard to see once I opened it up, but replaced 16x injector o-rings and also did the lower intake manifold (valley gasket) and also the end cap things. That sorted most of the vacuum leak and the rough idle!

Revs went down a bit too, and O2 codes went away, apart from these two codes I still have:

• P1171 - System too lean (bank 1) - Additive injector adaptive fuelling - lean limit exceeded LH bank
• P1174 - System too lean (bank 2) - Additive injector adaptive fuelling - lean limit exceeded RH bank

My long term O2 trim readings are now:

• Bank 1: 5.47%
• Bank 2: 5.47%

MAF air flow rate is still low at idle: ~20kg/h

I've still got a vacuum leak at:

1. throttle body spindle (videos)
2. brake booster to intake manifold connector (you can see it in this thread videos)
3. throttle body to plastic airbox connector (a new one... gonna use some plumber's tape to seal that off)
4. also the breather hose for the charcoal canister (but that's normal eh?)

I'm hoping that fixing #2 and #3 will remove the codes and that I won't have to replace my throttle body (#1).

 

Wow, that's great! Thanks for the update!

I suspect I have the same issue with my injector o-rings. What did your o-rings look like when you replaced them? Were they brittle or otherwise clearly a source of a leak?

Thank you for documenting everything so well and sharing it here for us to learn!

 

Pleasure mate!

They were so brittle. Most just cracked when I was prying them off. I suspect it was more the orings than the gasket.

I also noticed some have become kind of more cylindrical than rounded. They had like straight edges, while the new ones I was fitting were like little round donuts.

Here are all the buggered ones:

 

I now have no error codes and my Discovery II runs much smoother!

After thinking it through and determining that my O2 codes must be coming from a vacuum leak somewhere, I used the cigar smoke method to try to locate a leak, but could not identify any. This told me that none of the main areas of suspicion were the source of a vacuum leak. After dwelling on this for a while I remembered that when I replaced my fuel pump five years ago I ordered the non-EVAP compatible model by mistake, and foolishly thinking it would not cause issues I installed it and left the hose to the charcoal canister disconnected....

So naturally, ever since then, my PCV valve has been pumping air into the intake stream from the open end near my fuel tank. To confirm, I disconnected the PCV vent hose from the throttle body and temporarily sealed the nipple/hole with a tight rubber cap. The error codes for the front two O2 sensors immediately went away and it started idling much smoother!

However, the rear two O2 sensors were still throwing codes, so I replaced them both with a spare set I had from Amazon. Upon removing them I saw that the old ones were totally clogged up from years of running rich... with the new ones installed, those codes went away too!

I have now put over 80 miles on it since making these changes, and it has yet to throw any codes! It has also been running smoother as I drive more, which I attribute to the ECU adjusting to the absence of a vacuum leak.

I went through many phases of troubleshooting with this issue, and I'm ashamed to reveal that I allowed it to persist for so long, but I'm glad to finally have it resolved, and very thankful for all of the input from members of this forum! Now all I need to do is install the proper fuel pump and reconnect the PCV hose!