Bad fuel will not cause these codes. Also, using a higher octane than 8
in this vehicle will result in a lighter wallet with no benefit in mos
cases.
P1123 indicates that the computer thinks the engine has a rich fue
mixture and is leaning it out. The pinging could indicate a lean mixture
I see from the previous thread that you've already replaced the leakin
components of the exhaust. Now, if you haven't yet verified the operatio
of the oxygen sensor that was installed just before this code occurred, yo
should go back to that step.
Otherwise, the potential causes of P1123 I mentioned earlier still apply:
http://talkaboutautos.com/group/alt.autos.hyundai/messages/37541.html
Also, I see that the P0422 code has returned as expected. You probabl
need a catalytic converter. In fact, it's possible you should start wit
the converter rather than the oxygen sensor. If it's clogged enough, i
could restrict the exhaust to the point of excessive combustion chambe
temperatures and confusing the fuel management system