Running FULL rich, I think

[Dave 53]

Had a great weekend at Willow Springs Raceway, CA (1:38.9 best for those that know the track). Left happy and about an hour into a 5 hour drive home, my 818 started to run like ****. Kind of sputtering. Got behind a slow moving big rig and limped it home. Gas milage went to about 7 mpg, so I'm thinking for some reason the ECU went full rich. Was tough to restart after stopping and I wasn't sure I would make the last 2 miles into my garage. No check engine light or recorded OBD codes.

Bad O2 sensor? Bad or dirty mass air sensor? What's wrong?

Note: I have 1 O2 sensor. The second one was deleted and ECU was tuned accordingly. So, if the ECU normally compares the reading of the OEM 2 O2 sensors and triggers an OBD code based on that, mine doesn't. Two tuners I talked to said the second O2 sensor isn't used in the running of the motor, or something like that... So, a bad O2 sensor and no check engine light might make sense.