Manufacturers have confirmed there is a rough idle problem with a small number of 2.0-liter Boxer four engines and traced the problem to the engine's ECU. Automotive News reports while they have both arrived at the same conclusion, their actions to correct the problem are significantly different. The Subaru camp is fixing the ECU mapping snafu with a simple reflash while Toyota is resolving the issue with a full ECU replacement on vehicles with more than 100 miles on the clock. Either way, any cars sold after August 2012 should have no mapping anomalies.
2.0-liter Boxer Four Engine ECU Problems - Idle Chit-Chat: FR-S/BRZ Issues