Sometimes the Check Engine Light illuminates because the computer detects misfires. Subaru released an improved spark plug wire set to solve the problem. The ignition coil should also be inspected for carbon tracks or short circuits between the contacts
Engine Misfire Due to Failed Spark Plug Wires on Subaru Impreza WRX
Average mileage: 97,500 (30,000–174,000)
Engines affected: 2.0L 4 Cylinder Turbo, 2.5L 4 Cylinder Turbo
11 people reported this problem
My check engine light will blink and then go off and then a few days later it will be stay illuminated. I have checked the problem with the code reader and its says misfire and it always gives a different spar plug #. I just had these replaced less than 6 months ago there should not be any issues!!
2008 Subaru Impreza WRX - 2.0L 4 Cylinder Turbo 34,000 mi, Visitor
Since new dealer has not been able to solve problem...suggests valves are carboned crusted