Better MPG with higher octane = something is wrong with engine???

[joecar]

No, they will not throw any codes, their response has slowed down, but it is still within the PCM's test limits (older cars had looser limits).

[LB72004]

No, they will not throw any codes, their response has slowed down, but it is still within the PCM's test limits (older cars had looser limits).

Bingo, that just might be it. i guess i would have to monitor the voltage/reading on them and see what i get. any clue what i would be looking for? or is it just better to replace them?

if i remember right, he has something like 120 or 130 something thousand miles on it now. he was also talking about replacing the plugs for the first time. if that was the reason then it wouldn't explain the bad mileage when it was driven off the dealer lot.

[joecar]

If the NBO2's have 70K+ miles on them they usually are worn out.

I would also change the plugs much earlier, maybe every 50K miles.