Yours got it with the IAT removed? We've noticed a reaaaaaally weird lean spike on the dyno on my car... then recreated it with an untuned car.
What happens is at 2k rpm, at part-throttle (maybe 1/4 to 2/3), the car would go silly lean for some odd reason... hold it there on the dyno, and it would go so lean that it would bog... then finally the ignition would advance some and the fuel mapping would bump back up.
These ECUs are freaking weird. Don't know if this is what's happening to you US OBDII guys, but a trip to the dyno with a Scangauge tool should show whether this is what's happening to you. We think it's some strange closed-loop imperfection inherent to the cars.
Which is why we just unplug the O2 sensors and leave it be.