Engine light has two diag codes

[bluesboyst]

My 2000 Towncar is blowing out 2 diag codes. P0171 and P0174. The codes state that it could be either the Mass Air FLow Sensor or an oxygen sensor. I tried cleaning the MAF but it really did not help. Also you can hear the pinging in the engine like there is bad fuel.

Would these two codes show up if only one oxygen sensor is bad?

[Airjer_]

The very first thing I look for when I see lean codes on both banks is vacuum leaks.

[bluesboyst]

Hi,
Well I took your advice and started to look around for lvaccum leaks. I found that the PCV valve was not seated properly. When I would start the engine it would idle rough for about 10 seconds. Once I fixed the PCV it was fine.

It is running well now. I took off the negative battery cable to reset the engine light and it has not come back on. I drove the car at least 80 miles.

Thanks,

Steve