Maybe your O2 sensor just went bad?
I doubt the low concentration of acetone had anything to do with it.
Dunno for sure yet. I had the parts monkey reset the Code. So far it hasn't come back on yet (after 100 miles or so of driving).
Now bout the Acetone. I've read up on it's use extensively and have YET to hear any REAL Negative effects on vehicles fuel systems (OR O2 Sensors for that matter). The concentration is simply to low to cause corrosive damage to metal components of fuel systems. I never heard of O2 sensors going bad because of it, but thought my EX maybe one of the 1st!
There's just too much Positive proven proof facts out there to back up Acetone's positive effects on improving MPGs. The results are overwhelming to say the least. Yea, you here of folks that have had NO increases and some even decreases.
There's too many variables to pin down the exact cause of the negative effect of Acetone. My belief is that Acetone's effect REALLY comes into play during sustained Highway driving. Also, if one uses TOO MUCH acetone, it will negate the evaporative (or whatever property it's called) effect of acetone.
I've personally seen a 2-3 MPG INCREASE in my EX's Highway fuel mileage. It was obtaining around 19 MPG and is now obtaining 21-22 MPGs on a CONSISTENT basis.
So the decision for me is a No brainer. I will continue using Acetone and will tell everyone I can about it.