new to me prostar codes

[Nilao]

2791 is the egr valve fmi7 means no response so it's most likely stuck, I would pull it and see if it's full of soot causing it to stick. with 3 occurences start here...

spn 1209 is Engine Exhaust Gas Pressure Data Valid But Above Normal Operating Range - Moderately Severe Level....with 1 occurence I'd simply replace it and clean out the feed tube if you have not done so in the last year.

Intake manifold pressure sensor circuit data erratic....possibly from the sticking egr? Also replace it if it's more than a year old.

Reference this thread for guidance... http://rawze.com/forums/showthread.php?tid=34