Rough idle problem hits Scion FR-S, Subaru BRZ coupes

Toyota and Subaru are grappling with reports of rough idle and stalling conditions on their new sporty coupes.

The problems on initial batches of the Subaru BRZ coupe and its Scion FR-S twin--known as the Toyota FT-86 outside the United States--is being caused by a software mapping glitch.

Toyota Motor Corp. and Subaru, a unit of Fuji Heavy Industries, developed the sporty cars jointly. And except for some badging and front fascia differences, they are basically clones.

Toyota and Subaru officials say the problem is simply a software bug and that there is no mechanical defect.

But some owners of the coupes disagree, saying the suggested fix hasn't kept the problem from recurring.

Toyota spokesman Brian Lyons said that when the engine control unit (ECU) is installed, it adapts to the car's powertrain and owner's driving patterns, a process known as adaptive learning. Within 100 miles, those settings are basically frozen in the ECU.

With the Scion FR-S and Subaru BRZ coupes, some of the software coding that allows the ECU to establish a "handshake" with the engine is in error. The ECU monitors certain driving conditions, and when the engine is found to be out of tolerance, the software picks up an anomaly.

When this happens, the ECU triggers a fault code. As the ECU tries to find an optimal driving condition outside its prescribed tolerances, a rough idle or stalling situation ensues. Typically, the check engine light illuminates and a fault code of P0019 shows up on diagnostic readers.

Toyota's fix: If the car has less than 100 miles on it, a technician will reflash the ECU with the correct software mapping. If the car has more than 100 miles, the mechanic should replace the ECU.

"It does involve the variable valve timing but it does not involve a mechanical repair," Lyons said. He said the rough idle is the result of the ECU's attempting to work around its detection of the anomaly, rather than what is triggering the fault code. The reflash "broadens the tolerance of detection."

Subaru's explanation

Intriguingly, while Subaru agrees that ECU mapping is the cause, the automaker believes an ECU reflash is the only necessary repair.

"This is not a mileage-dependent condition. No replacement of the ECU is needed at any mileage to rectify the issue. The ECU re-flash is the fix. There is not a defect concerning the ECU," Subaru spokesman Dominick Infante said.

Toyota's ECU programming is being handled by field technical specialists, rather than dealership service techs, resulting in longer-than-normal repair waits for customers, Lyons said. "Our field offices are coordinating the remedies."

Lyons said all cars that have arrived at a dealership since mid-August should already be reflashed with the correct ECU software mapping. And not every car built before then will have the handshake issue, because "it's a combination of parts, tolerances and interactions between the car and ECU" that can trigger the fault.

The Scion FR-S shares its mechanics with the Subaru BRZ.

Angry customers

As performance coupes, these cars are attracting coveted enthusiast buyers and brand evangelists. But their vocal owners have not been pleased to see their vehicles underperform.

"Mine's on the third week in the shop. Parts are on back-order," a Scion FR-S owner in Washington state known as "Alrashwa" wrote on the FT86club.com Web site. "VVTi cam gear and oil control valve are what they claimed to be replacing. Waiting on gaskets which are on back-order, apparently."

Others on the forum say they have had replacements performed of the camshaft bearing, cam gears, actuators and cam position sensors.

Subaru's Infante called the condition "extremely rare." However, the FT86club had more than 100 registered complaints. What's more, several members who have had the ECU reflashed or replaced said the fix didn't stop the problem from recurring, resulting in other engine fault codes and additional service lane visits.

Toyota and Subaru officials declined to say how many cars could be affected or how many complaints have been filed.

By Mark Rechtin- Automotive News