Fast idle on start!

[trawfish]

I just finished a new 454MAG MPI with an M1SC Procharger. I have been working out the bugs, but right now I have an issue with start up. Every time I start the engine, it revs to 2000 rpm for litarally 5 seconds and them comes back down to around 850-900.

What could be causing this?

-ECU was reprogrammed for this set up.
-I swapped out IAC with another running engine and no change.
-No vacuum leaks present
-If I put code checker on and leave in diagnostic mode this does not happen.

[Perlmudder]

my engine is a lot smaller, but it revs to about the same but drops down to about 650 pretty quick. I just figured it was the efi doing its thing