It started right after I swapped tunes, check engine light came on right as I was pulling out of the post office sending my core back. I figured it was probably the Bosh o2's I had, unlikely they both fail at the same time, but stranger things have happened. So I swapped in these Densos, and same problem. Tightened them in till they were just snug with the wrench. Took it to a shop the other day after I looked at all the connections and fuses, they hooked up a scan tool and checked all the wiring. Only thing they could think was the computer, so I sent in for a new tune, which hopefully will clear up the issue.