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 noticed that my altezza's belts are suffering some wear and tear condition (rubbers starts to peel off) and my friend suggested that i should change the belts........:X-: