Please add this to your Immobilizer Problems sticky:
If I match my key/immobilizer to a new ECU (such as using KPRO in 05-06 RSX), can I return to my OEM ECU without matching again?
The short answer is no. Once you have matched your key/immobilizer to any ECU, it will only be programmed for that ECU. Although the ECU contains a database of acceptable immobilizers (1) and keys (5), the keys and immobilizer only retain the current ECU. If you match an ECU and want to swap to either KPRO or OEM, you will have to have the immobilizer and key matched at the dealer.