My first thought to reading that you may have solved it with a MAF and IAC is a little skeptical, thinking a bit further though......
The MAP sensor is the actual sensor reading that the change in EGR flow isn't sufficient. The pcm expects to see a certain change with various EGR positions and doesn't. To do this it must be using the MAF airflow info to expect a certain pressure then add the EGR opening to expect a slight change in pressure from what the calculations tell it to expect from the MAF readings.
If the MAF readings are false, then the map will not be able to read properly and potentially give a code for something that isn't actually happening.
Hopefully you got the problem solved.