You may want to install a new oxygen sensor then follow the previous suggestion. A new O2 sensor on a KA (CIS with frequency valve) or a KE (CIS-E with electrohydraulic actuator) fuel injection system does wonders. IMO-at 60K the sensors frequency has degraded, at 90K the switching time is too slow and it is time to install a new one. I have had lots of people argue about replacing the sensor however they sing a different tune when they experience decent engine performance with good fuel mileage.

You may have another issue but an O2 sensor at this point may be a good investment.