Washington ? Toyota’s top U.S. executive told lawmakers on Tuesday that he is not certain the company has fixed its runaway car problems even though it has recalled millions of vehicles around the world.

Although the automaker has blamed obstructing floor mats and sticky gas pedals for reports of cars accelerating out of control, lawmakers at a hearing on Capitol Hill appeared skeptical about the sometimes-conflicting accounts of what went wrong.

James E. Lentz III, president of Toyota Motor Sales USA, said recalls of popular Toyota cars and trucks still may “not totally” solve problems of sudden, unintended acceleration.

The hearing before the House Energy and Commerce Committee was jammed with spectators and media, who heard testimony about terrifying car rides, as well as engineering analysis and a corporate apology. Lentz once fought back tears recalling that he lost his brother in a car crash years ago.

At another hearing set for today, Toyota President Akio Toyoda plans to face the House Oversight and Government Reform Committee and attribute the company’s troubles to rapid growth.

On Tuesday, lawmakers heard testimony from a retired Tennessee social worker whose Toyota 2007 Lexus ES 350 sped up to 100 miles per hour during a six-mile ride in 2006. The car sped on even after the driver applied the emergency brake and shifted into neutral and then reverse.

For months, the couple tried telling their story to journalists, to Toyota and to federal safety regulators. One Knoxville television station, WATE-TV, ran a story. Toyota said the engine seemed fine. An investigator from the National Highway Traffic Safety Administration visited the couple, but “seemed to arrive with the preconceived idea to sell to us that it was a floor mat problem,” Smith testified.

It wasn’t until the death of a California Highway Patrol officer and his family in August that the company and regulators seemed to give more credence to complaints.

“Shame on you, Toyota, for being so greedy,” Smith said. “And shame on you, NHTSA, for not doing your job.”

The Tennessee couple was followed by David Gilbert of Southern Illinois University, a professor who said his interest was “piqued” after seeing reports about runaway Toyotas. Gilbert said he conducted an experiment that showed a Toyota Avalon’s onboard computer could be tricked into operating as if nothing was wrong even if the accelerator was stuck and the car was speeding uncontrollably.

Gilbert’s research was attacked by Rep. Steve Buyer, R-Ind., who has a Toyota assembly plant in his district. He asked Gilbert if he had “cut three wires” in the car to rig his test. Gilbert said he had not; he tapped into the wires with a monitor for electric current, a procedure within scientific methods.

Rep. Jane Harman, D-Calif., who owns between $116,002 and $315,000 in Toyota stock with her husband, recused herself from participating in Tuesday’s hearing.