NHTSA Administrator David StricklandNational Highway Traffic Safety Administration Administrator David Strickland has released a letter defending the agency's handling of investigations into claims of unintended acceleration by Toyota owners. Republican Senator Charles Grassley has said questions remain about what caused unintended acceleration instances in the Japanese manufacturer's vehicles, specifically whether or not the trouble was caused by electronic glitches. Grassley specifically questioned whether NHTSA had the experience necessary to diagnose the defect. The senator also wondered why NHTSA investigators called in NASA scientists for assistance during the investigation.

Strickland, meanwhile, has responded by saying NHTSA did, in fact, have the requisite experience and that NASA was called upon for a second opinion. The administrator underscored the fact that neither NHTSA nor NASA could find an electronic reason for the claims of unintended acceleration. As you may recall, the government agency concluded in early 2011 that faulty gas pedals and floor mats were to blame for the runaway syndrome.

According to The Washington Post, Grassley's letter stemmed from tips from whistleblowers who claim the runaway vehicles were actually caused by errant strands of solder within the pedal assembly itself. Those strands could reportedly cause shorts within the system.

Strickland responded by saying NHTSA investigated the solder issue, otherwise known as "tin whiskers," and found the issue to cause no more than a jumpy throttle, a stance Toyota agrees with.