Yes, I went through this firedrill a year or two ago and indeed it was the O2 sensor connector under the passenger floor mat.

Steve Brotherton said that when this happens, you can disable the EHA to see if the problem is with the mechanical or electronic portion of the FI. As it turned out, by chance I pulled the exhaust system for something else and found the connector to be flaky.

Glad you're up and going again,