While the Toyobaru engine has made its place in the ten winning engines of Ward's 10 Best Engines competition:
some units are still experiencing issues, no official numbers yet. Reflashing/replacing the ECU is the official answer to the rough idle and CEL issue though:
The problem is that Subaru and Scion customers who rushed in to buy the first batch of cars are now complaining about rough idle and stalling issues.
Toyota and Subaru announced that there’s no actual mechanical defect in the engine and the issue is caused by a software mapping glitch.
Toyota spokesperson Brian Lyons said that the engine control unit (ECU) is programmed to adapt to the car's powertrain and owner's driving patterns. Within 100 miles (160 km), those settings are “frozen” in the ECU.
Software coding errors in the ECU-engine communication are the culprits for this error. Under certain driving conditions (that were not specified) the electronic control unit software “thinks” that the engine is operating outside its “frozen” parameters and causes stalling or a rough idle as it tries, and apparently fails, to sort things out.
It then flashes the “check engine” light and when plugged into a diagnostic reader, shows a “P0019” error code.
The interesting thing is that, while both Toyota and Subaru agree on the nature of the problems, they offer different solutions.
Subaru will simply re-flash the ECU on all BRZs that have this issue. Toyota, on the other hand, will re-flash the ECU on the GT86 and Scion FR-S only if the car has less than 100 miles; otherwise, it will replace the whole unit.
"This is not a mileage-dependent condition. No replacement of the ECU is needed at any mileage to rectify the issue”, Subaru spokesman Dominick Infante told Automotive News. “The re-flash is the fix. There is not a defect concerning the ECU.”
Not all owners agree that the explanation of a software error is accurate, because even after they had their cars’ ECUs remapped or replaced, the problem keeps occurring claiming there is a mechanical issue.
Toyota and Subaru wouldn’t comment on how many cars are affected or how many complaints they have received until now.