Toyota assembled a group of experts to refute studies by an Illinois professor who revved Toyota engines simply by short-circuiting the wiring. Toyota's experts say the experiments were done under conditions that would never happen on the road.

The automaker maintained its assertion that simpler mechanical flaws, not electronics, were to blame.

"There isn't a ghost issue out there," Kristen Tabar, an electronics general manager with Toyota's technical center, told a news conference at the company's North American headquarters in Torrance, Calif.

Meeting with reporters, Toyota addressed the work of David W. Gilbert, an automotive technology professor at Southern Illinois University-Carbondale, whose work has been the basis of doubts about Toyota's mechanical fixes.

At least one outside expert said that even if Toyota's criticisms are accurate, the professor's work shows the systems that allow brakes to override stuck gas pedals can be compromised.

Toyota is mounting a public campaign to reassure its drivers about their safety and defending itself against critics who question the fix for 8 million recalled cars and trucks. Regulators have linked 52 deaths to crashes allegedly caused by the accelerator problems.

The company's fix addresses gas pedal parts and floor mats that can cause the accelerator to become stuck in the depressed position. More than 60 Toyota owners who have had their cars repaired have complained the problem has persisted.

Toyota dealers have fixed more than 1 million vehicles. But the government has warned that if the remedy provided by Toyota does not properly address the problem, federal regulators could order the company to come up with another solution.

Gilbert told a congressional hearing Feb. 23 that he recreated sudden acceleration in a Toyota Tundra by short-circuiting the electronics behind the gas pedal -- without triggering any trouble codes in the truck's computer.

The trouble codes send the car's computer into a fail-safe mode that allows the brake to override the gas. Gilbert called his findings a "startling discovery."

House lawmakers seized on the testimony as evidence Toyota engineers missed a potential problem with the electronics that could have caused the unwanted acceleration.

But Monday, Chris Gerdes, director of Stanford University's Center for Automotive Research, and a consulting firm, Exponent Inc., rejected the professor's findings.

Toyota's assembled experts said the professor's experiments could not be recreated on the actual road. For example, they said, Gilbert had shaved away insulation on wiring and connected wires that would not normally touch each other.

"There is no evidence that I've seen to indicate that this situation is happening at all in the real world," Gerdes said. He added that the professor's work "could result in misguided policy and unwarranted fear."

To prove their point, Toyota officials revved the engines of cars made by competitors, including a Subaru Forester and a Ford Fusion, by connecting a circuit rigged up to the wiring of the gas pedals.

Toyota supports other research programs at Stanford's engineering school and is an affiliate of the Center for Automotive Research, but Gerdes said he came to his conclusions "with complete independence."

Gilbert did not immediately respond to messages seeking comment.

Exponent has conducted work for companies that are being sued and once determined that secondhand tobacco smoke was not cancerous. It was also hired by the U.S. government to investigate the Columbia space shuttle disaster.

Exponent officials said they were conducting an extensive study of Toyota electronics but they had not yet found any problems with the electronic throttle controls.

Toyota has been steadfast in saying the problem is strictly mechanical. Company president Akio Toyoda assured Congress two weeks ago that Toyota research had not found a link between the reports of runaway acceleration and electronics.

Instead, the company is shortening gas pedals to prevent them from becoming lodged under floor mats and inserting metal pieces the size of a stamp to keep gas pedals from sticking in the depressed position.

An outside expert, Raj Rajkumar, an electrical and computer-engineering professor at Carnegie Mellon University in Pittsburgh who studies auto electronics, said Gilbert's work raises doubts about the fail-safe systems.

"Pretty much anybody who works on electronic-based vehicle systems understands that things can go wrong," he said.

He said a number of factors could cause vehicle electronics to malfunction, including software coding errors, electrical interference and static electricity. He said technology wasn't available to prove that a system as complex as Toyota's electronic throttle control will always behave correctly.

The professor wasn't trying to prove that his test was a real-world scenario, said Keith Armstrong, a British electronic engineer and consultant who advises companies on electromagnetic interference. Instead Gilbert demonstrated that fail-safe systems may not kick in if faulty signals are sent to the throttle, Armstrong said after reviewing Exponent's report on Gilbert's tests.

Congress has more questions. The House Oversight Committee wants to look at a 2006 memo from company employees to Toyota senior management that raised concerns the automaker was taking shortcuts on safety.

In the memo, first reported Monday by the Los Angeles Times, the employees said they were concerned the processes used to build safe cars might be "ultimately ignored."

The employees warned that if Toyota failed to act, it could "become a great problem that involves the company's survival."

Toyota executives also plan to address recall issues at the company's annual suppliers meeting in Kentucky on Tuesday.