P0171 ecu code - mix too lean bank 1

[mscmor]

About a month ago the "service engine soon" light set in my 2000 max.

I took it to the dealer and they confirmed code P0171 and replaced the oxygen sensor @ $275.

Two days later the light came on again. I took the car to autozone and found P0171 was back. I returned to the dealer and they replaced 2 intake manifold gaskets. the service was valued @ $249. I have 52,000 miles and however, they said the service was covered by warranty (yes that was a shock), no charge.

Two days later P0171 was back once again, this time along with P0174 - mix too lean bank 2. Once again back to the dealer and the mass airflow sensor was replaced as a cost of $211. Since then I notice significant improvement in running performance. Feels like the motor has been tuned up.

I went up through the chain of management and could not get the service manager to refund me my $275 for the oxygen sensor they originally replaced. I feel replacing the oxygen sensor was a mis-diagnosis.

Any way, I wanted to mention the general feel of the care was poor accelerationi at times, a loud knock under heavy acceleration and poor acceleration from cold starts (felt like I was running on 4 cylinders some mornings for the first quarter mile or so).