WASHINGTON - A House committee on Friday questioned the rigor of Toyota's sudden acceleration tests, challenging the automaker's commitment to finding the causes of safety problems that have led to millions of recalled vehicles. Other lawmakers zeroed in on federal investigators' response.

The House Energy and Commerce Committee told Toyota executive Jim Lentz in a letter that there is "an absence of documents" to show whether the company thoroughly investigated the possibility of unintended acceleration. The committee asked who is involved with the testing and demanded that it be given quarterly reports detailing allegations of the unwanted acceleration.

"We do not understand the basis for Toyota's repeated assertions that it is 'confident' there are no electronic defects contributing to incidents of sudden unintended acceleration," wrote Chairman Henry Waxman, D-Calif., and Rep. Bart Stupak, D-Mich.

Also Friday, House Oversight and Government Reform Committee Chairman Edolphus Towns, D-N.Y., and Rep. Darrell Issa of California, the panel's top Republican, asked NHTSA for more details on steps the agency is taking to address the acceleration issues and for more information on the number of complaints by Toyota drivers.

Toyota has recalled more than 8 million vehicles worldwide to address gas pedals that can become sticky or trapped under floor mats, prompting scrutiny from Congress. The world's No. 1 automaker has said it is investigating reports of sudden acceleration but remains confident there are no problems with Toyota's electronic throttle control systems.

Adding to the doubts, the government has received more than 60 complaints from Toyota owners who had their vehicles fixed following the recalls but say they've had more problems with their vehicles surging forward unintentionally. The National Highway Traffic Safety Administration is looking into the claims.

Toyota dealers have been fixing the accelerator pedals. But NHTSA said Thursday that if the remedy provided by Toyota is not addressing the issue, the government could order the company to provide a different solution.

Toyota spokeswoman Cindy Knight said the automaker will cooperate with the committee's request and is "quickly investigating verifiable complaints" from drivers about sudden acceleration. The company is already updating the committee on a regular basis, she said.

Toyota hired a consulting firm to study whether electronic problems could cause unintended acceleration. The firm, Exponent Inc., released an interim report that has found no link between the two. But committee investigators have said the Exponent test was flawed because it studied only a small number of Toyota vehicles.

David Gilbert, a Southern Illinois University-Carbondale professor, testified before the committee last week that he was able to create sudden acceleration in a Toyota by manipulating the vehicle's electronics. Knight said Toyota will provide the committee with Exponent test results that will disprove Gilbert's conclusions. Toyota said it was able to do the same with vehicles made by competitors and that Gilbert's tests do not replicate "real world" conditions.

In the letter, Waxman and Stupak also request more details on brake override systems and "black box" information in Toyota vehicles.

Toyota plans to install brakes that can override the gas pedal in future models and many vehicles already on the road. The safety measure is meant to prevent the unintended acceleration that has caused some Toyota drivers to speed out of control.

The committee also wants to know what information is available in Toyota electronic data recorders. The "black box" information could help investigators learn more about what is happening in the vehicles before crashes.

NHTSA has linked 52 deaths to crashes allegedly caused by Toyota's acceleration problems.