I found out today while finishing up an f20b swap into a 2000 Prelude race car that the iab solenoid and PCB ecu on a JDM f20b works the opposite of a USDM H22 iab solenoid. The PCB ecu grounds the iab solenoid at around 4800 rpms and above rather than at idle up to 4800 or so like on the h22 ecu. The f20b solenoid releases the vacuum when grounded to open the secondaries. The f20b solenoid part number is 36163-PCB-004. I switched the vacuum line from the bottom port of the solenoid to the vent filter port and moved the vent filter to the bottom port of the h22 solenoid to make it work as i dont have the f20b vacuum tank and solenoid. This holds the secondaries closed even when engine is off and opens them at 4800. from what im seeing, thats how honda designed it to work on the sir-t. Im sure this will add to the iab confusion but hopefully it helps a few who are puzzled by the backward operation of the iab when using the PCB ecu.here is a simplified layout of the bacuum connections. The blue bottom port of the solenoid is now the vent. As far as i know this is only on the f20b, possibly the H23a.

 

Here is the vacuum diagram for the f20b. Its plumbed the same way mine is now