Illinois engineer David Gilbert testified on Capitol Hill last month that he recreated sudden acceleration in a Toyota vehicle by manipulating its electronics. The automaker rebuffed his claims Monday, saying Gilbert's laboratory scenario was 'highly unlikely to occur naturally.' (Associated Press)

Toyota gave detailed evidence Monday it says disproves claims that faults in the electronics used in its vehicles are behind the acceleration malfunctions that led to the recent recall of more than eight million cars and trucks.

Toyota was attempting to counter tests by Southern Illinois University-Carbondale engineering professor David W. Gilbert, who said Toyota engines could rev without a driver pressing on the gas.

The automaker says mechanical problems, not electronics, are to blame.

Gilbert, who specializes in automotive technology, had tampered with wiring to create electronic glitches that could never occur on the road, said Chris Gerdes, director of Stanford University's Center for Automotive Research and the consulting firm Exponent Inc.

Gilbert's work "could result in misguided policy and unwarranted fear," Gerdes said.

Mechanics, not electronics, led to problems: Toyota

Gilbert's experiments have been the basis of many doubts that Toyota's mechanical fixes for the sudden acceleration that has occurred in some of its vehicles will truly solve the problem.

The professor 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.

"We do not believe that electronics are at the root of this issue," Mike Michels, a Toyota spokesman, said during a demonstration at the automaker's North American headquarters in Torrance, Calif.

Toyota says faulty gas pedals and floor mats, not electronics, are the cause of the acceleration problem. It is currently correcting those issues in millions of vehicles. But some drivers have reported continued problems in vehicles that have already been supposedly fixed.

Federal safety regulators are investigating complaints over Toyota's repairs. Michels said the automaker is also reviewing the complaints and that some were the result of bad repairs or other factors.

Gilbert told Congress he made a "startling discovery" that showed the electronic throttle control system could have a problem without producing a trouble code. The code sends the computer into a fail-safe mode that allows the brake to override the gas.

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

Electronics tampering unlikely to occur on road

According to Exponent, Gilbert connected sensor wires from the pedal of a 2010 Toyota Avalon to an engineered circuit, revving the engine without using the pedal. Gilbert demonstrated the method in an ABC News story last month.

Exponent said it reproduced the test on the same model year Avalon and a 2007 Camry and was able to rev the engine. But it concluded the electronic throttle system would have to be tampered with significantly to create the right conditions.

"Dr. Gilbert's scenario amounts to connecting the accelerator pedal sensors to an engineered circuit that would be highly unlikely to occur naturally, and that can only be contrived in a laboratory," an Exponent report said.

For example, Exponent said, Gilbert stripped wires in Toyota gas pedal systems of their insulation and used circuits to connect wires that were too far apart to touch each other.

Exponent said it also revved the engine of some Toyota competitors' cars using the same technique, including a Subaru Outback and a Ford Fusion. The automaker stressed its tests did not show any flaws with those models or its own cars.

Toyota's event Monday is part of a broad campaign by the world's biggest automaker to discredit critics, repair its damaged reputation and begin restoring trust in its vehicles.

In Canada, 270,000 Toyota vehicles were recalled. The company has two assembly plants in southern Ontario that employ a total of around 6,500 people. Toyota Canada builds the Corolla, the Matrix and the Lexus RX350 in Cambridge and the RAV4 sport utility vehicle in Woodstock, all for domestic consumption and export to the U.S. market.

On Friday, a congressional committee questioned Toyota's efforts to find the causes of the problems. It also questioned whether the company had sufficiently investigated the issue of electronic defects.

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