What did you do with whatever else you've got?

[Dead Eye]

The major problem is behind any of the O2 sensors but I'll admit the manifold connection could be a problem...

I'd like to rule out as many of the other possibilities as I can first though as I'd prefer to get the exhaust changed without this as a problem to ensure any tuning isn't skewed.

Also, wouldn't the O2 sensors trigger an engine management light? I guess this is technically at the other end of the spectrum for readings but still...