Some 2012 – 2013 model year iQ vehicles may exhibit one or more of the following conditions: Rough idle condition. Idle speed momentarily drops at idle. MIL “ON” with one or more of the following DTCs: P1603, P1604 and/or P1605. A new Valve cover along with the TSB repair procedure has been developed to address this condition, part number 11201-47121 Genuine Toyota Fluid 00289-1TE00 Top Engine Cleaner These codes may be caused by excessive carbon build-up on piston head. Follow the Repair Procedure in Technical Service Bulletin 0008-16 to address this condition.