Theories continue to abound to explain the unintended acceleration issues that prompted a massive recall of 8.5 million Toyota models globally, touched off a Congressional investigation, and created a public relations nightmare for the Japanese automaker.

Now, two British engineering consultants set to meet with investigators in the United States, are suggesting electromagentic interference (EMI) as the culprit, citing parts of the pedal assembly and electronic throttle-control systems on affected models that lack EMI shielding.

One of the consultants, Keith Armstrong, speaking at a news conference in Washington organized by consumer advocates, said, "Thirty years, empirical evidence overwhelmingly points to (sudden acceleration) being caused by electronic system faults undetectable by inspection or testing."

Testing by automakers, including Toyota, does not cover real-life EMI interference situations, Armstrong said, nor does the testing simulate the typical faults necessary to verify the functionality of backup measures.

In response, a Toyota spokeswoman, Cindy Knight, said, "They said all automakers electronics are subject to faults due to EMI, none of the automakers have designed systems that can detect it, much less prevent it, no automakers have properly shielded their electronics or designed fail-safes or black boxes or brake override systems that actually work reliably."

"Toyota has sold more than 40 million cars and trucks with our electronic throttle control system (ETCS) and we are very confident that the system is not the cause of unintended acceleration," she said. "Toyota engineers have comprehensively tested our ETCS under both normal and abnormal conditions including electromagnetic interference, and we have never found a single case of unintended acceleration due to a defect in the system."