SAN DIEGO — The mystery surrounding a Toyota Prius whose driver reported a stuck accelerator deepened Sunday as the motorist’s attorney dismissed a congressional memo that questions his client’s version of events.

The memo said technicians with the National Highway Traffic Safety Administration and Toyota could not duplicate the sudden, unintended acceleration that James Sikes said he experienced March 8 when he reached 94 mph on a California freeway. Investigators tried during a two-hour test drive Thursday.

The memo was based on a congressional staffer’s observations of a two-day inspection last week at a dealership in suburban San Diego. A Toyota official who was at the inspection explained that an electric motor would “completely seize” if a system to shut off the gas when the brake is pressed fails, and there was no evidence to support that happened, according to the memo.

“In this case, knowing that we are able to push the car around the shop, it does not appear to be feasibly possible, both electronically and mechanically that his gas pedal was stuck to the floor and he was slamming on the brake at the same time,” according to the report for the House Committee on Oversight and Government Reform.

Kurt Bardella, a spokesman for the committee’s top Republican, Darrell Issa of California, said Sunday that the findings “certainly raise new questions surrounding the veracity of the sequence of events” reported by Sikes.

“We’re not saying Mr. Sikes is wrong or that he lied, we’re saying that questions have arisen in the investigation,” Bardella said.

John Gomez, Sikes’ attorney, said the findings fail to undermine his client’s story.

“I don’t put a whole lot of stock in their explanation,” he said. “It’s not surprising they couldn’t replicate it. They have never been able to replicate an incident of sudden acceleration. Mr. Sikes never had a problem in the three years he owned this vehicle.”

Brian Pennings, a spokesman for the California Highway Patrol, said his agency’s view that there is no evidence of a hoax is unchanged.

Toyota has recalled millions of cars because of floor mats that can snag gas pedals or accelerators that can sometimes stick.

The Prius is powered by two electric motor-generators and a small gasoline engine, all connected by transmission gears. A computer, which Toyota calls the “hybrid control computer,” determines what combination of motors is needed and which would be most efficient.

Craig Hoff, a professor of mechanical engineering at Kettering University in Flint, Mich., said that for the Prius to accelerate out of control, at least two systems would have to fail simultaneously. They are the sensor signal that tracks the brake and gas pedal positions when the driver presses on them and the hybrid control computers.

“The chance of them both going wrong, plus the fact that the signal is bad, it just seems very, very, very remote,” Hoff said. “Could it happen? Statistically, yes. But it just doesn’t seem very likely.”