[tholyoak]

Based upon the description of how the oil tank is plumbed, I don't see how it is providing a source of false air. My understanding is you have the breather hose from the case connected to the oil tank, the other connection at the tank is vented to the atmosphere to allow the case not to create a vacuum. The port on the throttle body boot that would normally connect to the tank is plugged. Thus no air leak on the intake side.

Have you checked or eliminated the IAC valve as the culprit. I can imagine if it is stuck in the open state it will continuously leak air past the throttle plate and result in a lean mixture.

Based upon your resistance values I don't think there is anything wrong with your CHT sensor. As stated above, mucking about with resistors to simulate different engine temps is just allowing for compensation of the lean mixture you have when the DME knows the correct engine temperature.
Again, this is all based upon the idea that you have a lean mixture that cannot be compensated for within the AFM adjustment screw.

-Todd