Some owners of the Subaru BRZ and Scion FR-S twins have been experiencing a rough idle – both manufacturers have acknowledged the problem and traced it to the ECU, but are going about fixing the issue in different ways.
According to Automotive News, the rough idle is linked to the boxer-four's electronic control unit, which will throw a fault code when it detects an anomaly in the variable valve timing's actuation under certain driving conditions. Both Toyota and Subaru acknowledge that as the source of the problem, but Subaru says that it is a simple software fix and Toyota is requiring some replacement parts.
Subaru says that the rough idle stems simply from an ECU mapping issue, and that reflashing the unit will resolve the issue. However, Toyota says that doing a reflash will only work on vehicles with less than 100 miles – the initial break-in period for the ECU. If an car has more than 100 miles, the automaker is requiring the ECU be completely replaced. AN reports that this is causing frustration with owners, as Toyota is sending field techs to complete the ECU fixes and taking longer than a regular repair. Some owners who have had their ECUs reflashed or replaced are still reporting the rough idle issue, as well.
Any cars that arrived at dealerships starting in mid-August should already have the correct ECU software mapping, according to AN, but that not all vehicles may be affected. Subaru said that the problem was "extremely rare", although neither automaker will disclose how many units they think are affected.
Source: Automotive News (Subscription required)