After a crash that killed four people in California, drivers are asking for action from Toyota and Lexus to prevent another tragedy. The car maker has blamed the cars' sudden acceleration on floor mats, but drivers disagree.

In September Toyota recalled 3.8 million vehicles because of problems with gas pedals that got stuck on floor mats.

Now the National Highway Traffic Safety Administration said it is still investigating what it calls a "very dangerous problem." And the U.S. Department of Transportation told ABC News that the "removal of the mats is simply an interim measure, not a remedy to the underlying defect in the vehicles."

Team 5 Investigates' Susan Wornick discovered a former driving school instructor from Massachusetts whose car had this problem several times while driving newer-model Toyota Camrys.

"It was terrifying," said Steve Smith. "The first couple of times it happened I thought the students were not following instructions."

"It happened to me about four times. There was something wrong with the way the car responded. When you removed your foot off the gas pedal, it did not go back down to idle. It continued to accelerate," he said.

Smith's experience is not unique. Team 5 Investigates has confirmed an estimated 2,000 reports to federal safety officials of sudden, unintended acceleration with their Camrys, Lexus and Prius models.

"This is probably a driver's worst nightmare," said Sean Kane, an auto safety expert with Safety Research and Strategies in Rehoboth, Mass. "When the car can't be controlled and it's accelerating outside of your input. That's one of the most dangerous scenarios you can put yourself into in a car"

Toyota blamed incorrect installation of driver side floor mats and recently sent letters to Toyota and Lexus owners, warning them.

"I took the floor mat out and put it in the trunk just to alleviate that possibility, and yet it still continued to happen," said Smith.

An investigation by the National Highway Traffic Safety Administration failed to turn up any electronics defects in Toyota vehicles. But after hearing reports from hundreds of Toyota owners, the Department of Transportation has released a statement saying the matter is not closed.

Toyota told Team 5 Investigates Wednesday the company is continuing its investigation to make sure there isn't a problem with the gas pedal.

"A situation like this can make the difference between life and death," said Smith.

Safety experts told Wornick that drivers who experience this sudden, uncontrollable acceleration should put the car into neutral and slam on the brake. Don't turn off the car, they say, because doing so would cause drivers to lose power brakes and steering, which could exacerbate the situation.

Drivers who experience any problem with any vehicle should report safety concerns to the federal government via NHTSA's Web site.