CEL Code 11, newish O2 sensor

[Tylinol]

Hi everyone. I've got an intermittent CEL problem on my 1g 4G37 (1.8) that has become constant in recent days. Previously, the CEL would come on every couple of weeks for about ten minutes or so while driving, and then go off without any apparent symptoms. Eventually it started staying on more and more, and then constantly, at which point I replaced the O2 Sensor. After a brief drive, the CEL went off and stayed off. This was about nine months and 15,000 miles ago.

Last month it started coming back on again. This time I noticed that the car would stumble while driving while the light was on, and smooth out again when it went off. This past week it has stayed on constantly and is definitely not running on all 92 ponies. I've also noticed a drop in fuel economy - from 35-38 to 32mpg.

In both cases, I've been pulling CEL code 11 - O2 sensor. When I replaced the O2 sensor, I ordered the Denso part, which came highly recommended. So, if I were to assume that the O2 sensor is not the problem, what other issues could be causing my CEL and rough running?

Thanks

 

[Tylinol]

I don't think so, I ran the codes again and the only thing flashing was code 11. I'm getting suspicious of the O2 sensor, although I did notice a small ring of fluid (probably gasoline) along the outside of 2 of my injector seals. I will replace these this weekend.