WASHINGTON — House lawmakers on Thursday accused Toyota of failing to keep its promise to get to the bottom of what caused sudden unintended acceleration in some of its vehicles, despite public statements the automaker made to reassure consumers.

Rep. Henry Waxman, who chairs the House committee investigating Toyota's massive recalls, accused the automaker of relying upon a consulting firm which had conducted a limited review of potential electronic defects and whose mission is "to obfuscate and to find no problems."

"Toyota has repeatedly told the public that it has conducted extensive testing of its vehicles for electronic defects. We can find no basis for these assertions," said Waxman, D-Calif. "Toyota's assertions may be good public relations, but they don't appear to be true."

Jim Lentz, Toyota's top U.S. sales executive, said the company had no evidence that electronics are to blame for the sudden acceleration reports. Toyota has said mechanical problems have been addressed by its recall of more than 8 million vehicles.

The world's largest automaker has paid a record $16.4 million fine for a slow response to an accelerator pedal recall and faces hundreds of state and federal lawsuits. The Transportation Department could assess more penalties if it finds evidence the company delayed other recalls.

Toyota's safety concerns have led to the first major review of U.S. auto safety laws in Congress since the large tire recalls by Bridgestone/Firestone in 2000.

David Strickland, the head of the National Highway Traffic Safety Administration, said his agency had spoken to nearly 100 vehicle owners who said they had unintended acceleration following a recall fix.

But he said NHTSA had not seen pedal entrapment or sticky accelerators in vehicles that have been properly repaired. Strickland said the government was continuing its investigation, with the help of NASA scientists, into acceleration problems.