Typically, yes. When the ecu sees a lean mixture from the O2 sensor it will try to compensate by adding more fuel but cant compensate for more than a minor leak. Mostly you will see a lean mixture at ilde then it would correct itself at higher RPM. Thats not the case here From what I can tell from this, the O2 sensor is reading a rich condition and switching properly. Normal readings are typically around .1v Through .9v switching .4v to .8v shows a rich condition along with your LTFT reading of -24 (Rich). I would try swapping the FPR between cars. Edit: Plus having dry carbon/black build up on your spark plugs is an obvious rich condition. If the plugs stay wet and are black then you would have an oil issue. Light brown build up is a lean condition. With a -24 LTFT I wouldn't be surprised if you had black soot coming out of the exhaust at idle. Thats very Rich!