That could be your idling issue. It's BKR7EIX. See here - http://www.mkivsupra.net/vbb/showthread.php?41927-FAQ-Spark-plugs
I used to have the same issue years ago when BPU and increasing the plug gap a tiny bit fixed this (obviously you can't do this with iridiums)
Also, while you're fault finding, have you checked to see if there are any fault codes stored on the ECU? It's easy enough to do with a paper clip;
http://www.mkivsupra.net/vbb/showthread.php?35920-How-To-Check-the-diagnostics-codes
Once you've done that, it might be worth resetting the ECU. When you start the car afterwards, the ECU self learns for around 10-15mins (just leave it idling, don't drive it). It'd be interesting to see if that makes any difference to your idle problem.
Check for error codes first as resetting the ECU will wipe any stored codes