Mark Templin, Lexus Division general manager, said that an internal investigation shows that, “during the manufacturing process, some contaminated materials were used in the manufacture of valve springs which could involve noise or rough idlings, and even stall.”

Of the 270,000 engines involved, 170,000 are in the U.S., Templin said.

“We have had very few customer complaints related to this issue...less than 1 percent of vehicles affected,” Templin said. “It does not include vehicles selling now.”

No accidents or injuries have been reported, Toyota said, related to the stalling issue. Toyota said that in rare cases, the stall may occur while the sedans are being driven.

WASHINGTON -(Dow Jones)- U.S. regulators have yet to find any electronic defects in Toyota Motor Corp. (TM) vehicles, a U.S. vehicle-safety official reiterated Wednesday, as a scientific panel began studying potential causes of unintended acceleration.

Some members of Congress, consumer advocates and product-liability lawyers have suggested that engine electronics may have played a role in problems that led Toyota to recall more than eight million vehicles globally for sudden- acceleration and gas-pedal problems. Those critics have questioned the adequacy of efforts by Toyota and government regulators to study electronics.

"We have not actually been able to find a defect of electronic-throttle- control systems" in Toyota cars, said Dan Smith of the National Highway Traffic Safety Administration, speaking before a panel of the National Academy of Sciences.

He said regulators have only been able to identify two causes of the Toyota problems--floormat entrapment of the gas pedals and pedals that are slow to return to idle.

The academy is undertaking a broad study of unintended acceleration and will eventually offer recommendations on how regulators should improve their ability to set standards and identify defects.

Smith said his agency hasn't ruled out the possibility of electronic defects and that investigations are ongoing. NHTSA is working with NASA engineers to study the Toyota recalls, including possible electronics defects.

NHTSA chief David Strickland told the academy panel that unintended acceleration is a problem that affects all major car manufacturers.

"Complaints of unintended acceleration are not--repeat not--exclusive to Toyota," Strickland said.

Another NHTSA official, Roger Saul, told the panel that the agency has, since Toyota's first recall in October, received complaints of 64 crashes involving 78 deaths, some years ago. Regulators have been able to verify that only one of those incidents was caused by a vehicle defect, Saul said.

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UPDATE 8:25 p.m. ET: Toyota Motor just said in Tokyo that it will recall 270,000 vehicles worldwide next Monday to fix engines with a valve spring problem that could cause them to stall. Spokesman Paul Nolasco said said vehicles include seven models (years so far unspecified) of luxury Lexus sedans and Japan's popular Crown. Of the 270,000 vehicles, some 137,000 were sold in the U.S. Nolasco said Toyota will inform Japan's transport ministry of a recall of 90,000 vehicles there on Monday. The U.S. recall could be announced as early as today.