> Looking for opinions, I have an issue where the check engine light is
> coming on. I recently gave the car a tuneup which cleared the misfire
> codes it had, but now (1 week later), I have the following codes
> present:
>
> P1128 Long Term fuel trim too lean
> P0172 System Too Rich
> P0134 Oxygen Sensor Circuit - no activity detected (pre-converter
> sensor)
>
> I am guessing that the O2 sensor needs to be replaced, but will this
> also fix the other codes? I haven't detected any vacuum leaks that
> might be suspect. Any help would be appreciated. Thanks.

I'm not like a lot of the guys here -- just dumber, probably -- but I
tend to go with hunches, if they're supported by any evidence. In your
case, a dead O2 sensor would affect fuel mixture, so that would say to
me, "Go ahead and replace the O2 sensor and see what happens." Odds
are, it will fix the problem. If not, you can at least tell yourself it
was not a total shot in the dark, it was a supportable decision, and
what the hell, it looks like you needed a new sensor anyway.

I went ahead and replaced a mass-airflow sensor recently, due to a
fuel-mixture code. They have a reputation for failing, so I rolled the
bones. Sure enough, it did the trick. There's still room for
seat-of-the-pants mechanics in this computerized age.