Some cars which have been repaired under the Toyota recall system have had questions raised about the effectiveness of the repairs.

Whether Toyota's repairs will prevent the cars from speeding up on their own has been at the forefront of concerns for owners of the vehicles.

Complaints have nearly doubled in the past two weeks with over 100 drivers saying a dealer has made mistakes in applying one of the recall remedies.

Toyota has said it is confident in its repairs and has found no evidence of other problems, such as faulty electronics.

But the US National Highway Traffic Safety Administration has been contacting owners who have complained about their repaired vehicles.

NHTSA has discussed the issue with Toyota, which has promised it will try to improve instructions to dealers.

Toyota has recalled more than 8 million vehicles worldwide since October, after complaints arose over sticking accelerator pedals.

In many of the comments to the NHTSA from Toyota owners, there were claims that the sudden acceleration issue reappeared only days after cars were fixed at their local dealership.