Let me see if I can help you to answer your own question.
What engine management "system" is your car using? A Mustang or Crown Vic? (hint: The PCM is from a Mustang).
But I contend that it's unreasonable to expect any motor to perform well when there's an outstanding DTC. Best to always post the full DTC code as there are 1,000's of them and they each have a story to tell. However myself personally would never replace an expensive part such as a MAF sensor without first:
- Cleaning it with MAF cleaner.
- Ruling out an intake vacuum leak.
- Confirming that the O2 sensors are sending "reasonable" switching data.
- Confirming the fuel pressure.
- Double checking that the fuel pressure regulator intake vacuum reference line is connected and leak free.
- Testing it with an ODB2 scanner to confirm that it is actually sending bad data.
Note, You have a PI motor installed into a car with a PCM set up for a non-PI motor. The PCM will run this motor but it will not be able to take full advantage of the PI heads without a tune.
Here's some information that may help you.
ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/
Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/