They may be reliable, but there are growing concerns about the safety of Toyota vehicles, more than 3 million of which are facing a recall.

When Toyota announced the recall of more than 3 million vehicles, last month, the Japanese maker not only hoped to ensure the safety of its owners, but to put to rest concerns about the safety and quality of its vehicles.

This week, recall notices will go out advising motorists how to deal with the problem which, according to Toyota, involves driver floor mats that can jam the accelerator pedal and make it difficult to impossible to maintain control of the vehicle.

But could there be another problem causing some Toyota products to surge out of control and, at times, race to speeds of up to 100 miles an hour?

That was clearly left open, today, when federal regulators issued a statement suggesting the 3.8 million vehicle recall is only an “interim measure, not a remedy.”

However, six times in the past six years NHTSA has undertaken a review of allegations of unintended acceleration on Toyota and Lexus vehicles, and six times the safety agency has found no vehicle based cause for the unwanted acceleration allegations.

According to Bob Carter, general manager of the Toyota division of Toyota Motor Sales USA, such a possibility has been dismissed by researchers for the National Highway Traffic Safety Administration, or NHTSA.  The problem is only caused by “out-of-position and inappropriate floor mats,” the executive said, earlier this week, and talk about other possible causes is simply “unwarranted speculation.”

But despite such assurances, there’s growing concern about the possibility of other issues with Toyota vehicles that can lead to so-called “unintended acceleration.”

A new report by ABC News contends that disbelieving owners are in “rebellion after a series of accidents,” unwilling to accept Toyota’s explanation and are seeking further action by government investigators.

“I’m absolutely certain that in my situation, it was not the floor mats,” Elizabeth James told the network’s news division. She was driving her Toyota Prius outside Denver, Colorado when she says it suddenly shot up to 90 miles an hour, even though her foot was on the brake and not the gas pedal.

While Toyota declined to discuss the issue with ABC, Carter spoke extensively with TheDetroitBureau.com, on Monday, and subsequently at a lunch meeting with reporters, in Detroit.  In it, he noted that the NHTSA did extensive tests to see, among other things, whether the computer systems controlling Toyota powertrains might be sensitive to interference from random electronic noise, such as from power lines or radio towers.

One of the victims who lost control of his vehicle was Bulent Ezal, whose Camry took off while driving along the coast in central California.  The vehicle plunged 100 feet off a cliff and into the Pacific Ocean, killing Ezal’s wife of 46 years.

“All of a sudden the car surged with force and I was thrown back to the seat,” said Ezal, who insists his foot was “absolutely, positively on the brake.”

Such complaints are reminiscent of the UA scandal that surrounded Audi products in the mid to late-1980s.  Hundreds of owners reported incidents in which the then-popular Audi 5000 sedan would suddenly surge out of control, racing forward no matter how much pressure a driver applied to the brakes.

A series of reports on the CBS News program “60 Minutes,” nearly killed the brand in the U.S.  But that network eventually retracted its strongly-worded allegations after NHTSA ruled out mechanical or electrical issues.  Though a specific cause of the Audi problem was never determined, experts at the time suggested it may have been the result of the 5000’s pedal design, which made it easy to reach for the brake but instead step on the gas.

For his part, Toyota’s Carter noted that “numerous” other manufacturers have and continue to face claims of unintended acceleration.  But reports like those on ABC’s “World News Tonight” threaten to tarnish the reputation of a brand that long prided itself on its quality and reliability.  Just last week, Toyota came out on top in the latest annual study of vehicle dependability by the influential Consumer Reports magazine.

Of course, it doesn’t help that Toyota is facing other problems involving potential safety defects.  A former corporate attorney, Dimitrios Biller, claims the automaker failed to provide internal documents to owners suing Toyota for alleged defects leading to rollover accidents.

“The average consumer on the street has little or no awareness” of the case, asserted Toyota division boss Carter, but some observers wonder if Biller might not wind up becoming Toyota’s Ralph Nader, a reference to the legendary consumer advocate – and failed presidential candidate – who stared down General Motors, in the 1960s, over safety problems with the Chevrolet Corvair.

One thing Carter said, this week is likely to be of little dispute.  As the automaker has gained sales and visibility, it is increasingly in the spotlight.  Problems that might have been ignored or relegated to the back pages of the business section now make the front page.

The death of a California Highway Patrol officer and three others, in an August crash involving a runaway Lexus, helped push Toyota to order the “voluntary” recall just getting underway.  And it led to an unusual apology from Toyota’s new president, Akio Toyoda, heir to the company’s founding family.  “Four precious lives have been lost. I offer my deepest condolences.”

But neither the recall nor that apology will likely end the growing debate over the safety of Toyota products, not if the latest announcement from Washington is any indication.  Government regulators warned today that the recall “is simply an interim measure, not a remedy of the underlying defects in these vehicles.”