Speed Control Linkage problems of the 1997 Toyota Previa

Unintended acceleration. Vehicle going ~50 mph on two-lane road. Accelerated rapidly to pass another vehicle. Passed at ~65 mph. Took foot off accelerator but vehicle continued to accelerate. Was able to bring to a stop. In 'park' engine also raced. Linkages checked, but were ok. Vehicle brought to Toyota dealer in flagstaff az. They could not find problem. Owner contacted Toyota twice. National customer relations told us to contact a dealer (again). Owner believes one contact was sufficient to show they cannot id problem. Wife driving at the time - accident barely averted.