Hopefully Darren can confirm this, but from what I understand the car appears to run fine except for the occasional Det warning at VERY high load (it did this occasionally when I had it too). Edit - not that I think Darren has used the car in anger since the problems began.
The AFR gauge is the one thats showing the lean condition, whether it's the one in the car or the Ryan's one.
Mark also mentioned that he thought one of the "turbo" gaskets is leaking (from a conversation with Darren this afternoon, it appears this is the one between the manifold and turbo).
So, we have two possible sources of O2 getting into the exhaust and causing a lean reading on the AFR gauge:
- coolant from a cartridge leak
- air from a gasket leak
One other posibility is a head gasket failure, however this seem unlikely as there is no sign of carbon in the coolant and the leakdown tests showed a healthy engine.
As the lean condition appears only once the engine is at full operating temperature this would tie with the two possibilities above (thermal expansion causing either to fail).
Thats the situation as I see it now.