My stock kouki blasts fire from under the car on decel (open downpipe, auto ecu).

Basically what you are hearing at 1500 rpms is the DFCO stopping (deceleration fuel cut off) so it starts fueling again below 1500 so the engine doesnt stall.

My Eclipse does that alot too...its kinda funny cause when I flash it while driving down the road it will shut the motor off, then when it finishes flashing the ECU it will kick back on and POP!. lol