Here's something that I never knew existed: Single Event Upsets. SEUs are the reason for technological glitches (usually in consumer electronics); they're caused by the resulting radiation when "cosmic rays strike the atmosphere". Could these radioactive waves be the cause of Toyota's unintended acceleration?
SEU glitches tend to show up and then simply disappear, leaving no hard evidence of the cause whatsoever. The major issue is that "unlike interference from radio waves, there's no way to physically block particles; [SEUs] typically have to be prevented by a combination of software and hardware design."