TOKYO — Feeling her Toyota Mark X station wagon lurch forward at a busy intersection, Masako Sakai slammed on the brakes. But the pedal “had gone limp,” she said. Downshifting didn’t seem to work either.

“I tried everything I could think of,” Mrs. Sakai, 64, said, as she recently recalled the accident that happened six months ago.

Her car surged forward nearly 3,000 feet before slamming into a Mercedes Benz and a taxi, injuring drivers in both those vehicles and breaking Mrs. Sakai’s collarbone.

As shaken as she was by the accident, Mrs. Sakai says she was even more surprised by what happened after. She says that Toyota — from her dealer to headquarters — has not responded to her inquiries, and Japanese authorities have been indifferent to her concerns as a consumer.