TOYOTA CITY, Japan -- Toyota Motor Corp. senior executives say the automaker is moving aggressively to improve quality after a recent rash of problems saddled the company with lawsuits, its largest-ever U.S. recall and allegations of deadly defects.

Toyota faces a series of cases involving rollovers, faulty steering rods and unintended acceleration. The latest blow came last month, when the National Highway Traffic Safety Administration said it would investigate complaints of rusted-out frames on Tundra pickups. That case involves an estimated 218,000 vehicles.

Separately, Toyota plans to recall 3.8 million vehicles for issues related to floor mats, accelerator pedals and unintended acceleration.

"We have to be more aggressive in terms of looking into the quality aspects of our operations," Yukitoshi Funo, an executive vice president, told Automotive News at the carmaker's headquarters. The former head of North American operations now oversees emerging markets.

Atsushi Niimi, executive vice president for North America and global manufacturing, said in a separate interview that Toyota is trying to improve the quality of both manufacturing and design. In part, that means re-engineering vehicles to withstand aging problems such as corrosion as customers hold on to cars longer.

Engineers also are trying to build more backup safety into designs. They are rethinking technology so that when breakdowns happen, dire consequences are less likely.

One item under review is the electronic start-stop button used in some Toyota and Lexus models in place of a key-operated ignition. The push-button ignition was cited in a recent NHTSA memo about an Aug. 28 accident involving a runaway Lexus ES 350 in San Diego that killed four people.

The memo noted that the button needs to be depressed for three seconds to turn off the engine, and that this instruction was not indicated on the car's instrument panel. A key-type ignition would have been able to stop the engine more quickly. Toyota is still trying to determine the cause of that accident.

Said Niimi: "We will also look into possibilities of incorporating designs that have more fail-safe functions and are more robust to try and prevent these kinds of tragic accidents in the future."

Takeshi Uchiyamada, executive vice president in charge of r&d, said during the Tokyo Motor Show that he believes some of Toyota's quality problems stem from the company's too-rapid expansion over the last decade.

"For many years, Toyota was trusted as a company for its quality," Uchiyamada said. "We must really work not to impair that trust."