The U.S. federal agency investigating Toyota's acceleration problems says it has not reached any conclusions about whether drivers may be to blame for their vehicles suddenly accelerating, a problem that has led to millions of recalled cars and trucks since last year.

A recalled Toyota gas pedal is posed next to a recalled Toyota Avalon. The agency investigating Toyota acceleration problems says it has not yet drawn any conclusions about driver errors. (Paul Sakuma/Associated Press)

The National Highway Traffic Safety Administration said in a statement that its engineers were continuing to investigate the possible causes of sudden acceleration in Toyotas along with scientists and researchers with the National Academy of Scientists and NASA.

The Wall Street Journal, citing anonymous sources, reported Tuesday that the government had analyzed dozens of event data recorders, or black boxes, in Toyota vehicles involved in crashes blamed on unintended acceleration and found the throttles had been open and the brakes not engaged. That would suggest the drivers were stepping on the gas pedal instead of the brakes.

'We will follow the facts and inform the public when our investigation comes to an end.'—Olivia Alair, National Highway Traffic Administration

Transportation Department spokeswoman Olivia Alair said government investigators had "drawn no conclusions and released no data. We will follow the facts and inform the public when our investigation comes to an end."

Toyota has recalled more than 8.5 million vehicles worldwide since last fall due to faulty accelerators, floor mats that can entrap gas pedals and brake problems in Prius hybrids. The Japanese automaker has sought to address problems with unintended acceleration by fixing the gas pedals.

Steering problems Toyota's latest woe

NHTSA is also investigating complaints by Corolla and Matrix owners about steering problems. Toyota spokesman Brian Lyons said Wednesday that the company notified dealers last month that it would replace the computers that oversee power steering if drivers ask for a fix.

NHTSA's investigation is continuing and Toyota has not issued a recall over the issue. About 500,000 Corollas and Matrix vehicles are covered by the federal probe.

The government has said unintended acceleration in Toyotas may have been involved in the deaths of 93 people over the past decade. The agency has received about 3,000 complaints of sudden acceleration in Toyotas.

Daniel Smith, NHTSA's associate administrator for enforcement, told a panel with the National Academy of Sciences reviewing unintended acceleration last month that the agency had not yet found any defects beyond the problems of pedals becoming stuck in floor mats and sticking accelerator pedals.

Toyota said Tuesday its own investigation had found a number of explanations for the sudden acceleration, including pedal entrapment by floor mats, sticking gas pedals and the misapplication of the pedal. The company said it had not found any cases in which the electronic throttle control was the cause.

NHTSA engineers have been investigating cases of sudden acceleration in Toyotas and studying vehicle electronics, working with NASA scientists to try to determine what caused the problems. The investigation is expected to be completed in the fall.

The National Academy of Sciences is conducting a broader review of unintended acceleration in vehicles across the entire auto industry. The panel is expected to report its findings in the fall of 2011.

Toyota paid a record $16.4-million US fine for its slow response to an accelerator pedal recall and is facing hundreds of state and federal lawsuits. Congress is considering an upgrade to auto safety laws in the aftermath of the Toyota recalls.