Spark Plug for 4AGE BT 20v engine is IK20.
For further information, u may refer this website
http://www.globaldenso.com/en/products/aftermarket/plug/basic_knowledge/heatrange/index.html
I've heard alot of issues on the GTT R34 HICAS. I've experience it once of the 5 months ownership of the car. How can we make sure that the light doesn't pop up again ?