2500 rpm is the safe mode on the nissans I know. My guess is you screwed up something on the install and it went into safe mode. Several things can go wrong
1 Maf on backwards (easy to do with a CAI)
2 Clip pluged into maf but not properly (or so you think), Unclip and put it back in.
3 Disconnected the TPS or some other item and forgot to put it back.

Look for these items and then reset the ecu. That should solve the problem. Unless you hit the maf or did something obvious its not likely that you broke the maf.