Complaints of sudden acceleration in Toyotas repaired under recalls have nearly doubled in the past two weeks, according to an Associated Press analysis of government data.
The complaints from 105 drivers raise questions about whether Toyota's repairs will prevent the cars from speeding up on their own or if there is another reason for the problem.
Toyota has said it is confident in its repairs and has found no evidence of other problems, such as faulty electronics. The automaker did not immediately comment Wednesday on the latest complaints.
The National Highway Traffic Safety Administration said it was contacting owners who have complained about their repaired vehicles. David Strickland, NHTSA's administrator, said in a statement Wednesday the agency has found "several instances in which a dealer made mistakes in applying one of the recall remedies."
He said NHTSA has discussed the issue with Toyota, which is trying to improve instructions to dealers.
Toyota has recalled more than 8 million vehicles worldwide since October over complaints that gas pedals can become sticky or trapped under floor mats.
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An AP review of a NHTSA database found reports of repaired cars continuing to accelerate on their own had jumped to 105 since March 4, when the government reported 60 such complaints.
The complaints are submitted online or through a NHTSA hot line and have not been independently verified.
In many of the comments, which can be filed anonymously, owners said the sudden acceleration issue reappeared only days after their cars were fixed at their local dealership.
"I went in for the recall and it seems there is a worse problem now," wrote the owner of a 2008 Toyota Tundra in Boynton Beach, Florida, who reported unwanted acceleration in early March. "I truly believe this is an electronic problem."
John Moscicki, of Lake Oswego, Oregon, told the AP his 2007 Camry accelerated on its own five times before he got the vehicle fixed under the floor mat recall last month.
On March 4, his repaired Camry took off from a standing stop on the freeway and accelerated to 50 mph before Moscicki managed to stop it by shifting into neutral, hitting the brake with his left foot and pulling back the gas pedal with his right.
"It just went to the floor like some other system had control of it," said Moscicki, who raced high-performance sports cars and previously owned a Porsche restoration business.
His Toyota dealer had the Camry for a week, and Toyota sent in a field engineer to examine the car without finding anything wrong. Moscicki said he had planned to give the vehicle to his college-age daughter but now intends to get rid of it. "I wouldn't let her anywhere near this car," he said.
The safety concerns are difficult to pinpoint because they could be related to any number of factors, said Diane Steed, who served as NHTSA administrator during the Reagan administration.
Besides telephone interviews with owners, the agency will look at how dealers fixed the cars, whether the problems involved common parts or the same manufacturing facilities or whether human error might be involved, she said.
Steed, who led the agency during a lengthy review of sudden acceleration complaints in Audi sedans, said there is no specific threshold that would automatically lead the agency to demand that Toyota, or any other automaker involved in a recall, come up with a new fix.
"It's really an engineering judgment call," she said. "The real challenge is not so much the numbers but digging to get to the bottom of what is the problem."