Ouch - no lubrication for a month and a half, then an instant 6,800
rpm. I'm surprised the engine didn't seize/explode. The throttle is
probably stuck open at the throttle body, leaving only the (rather
weak, by comparison) gas pedal return spring to keep the pedal from
simply flopping onto the floor. Unsticking the throttle at the engine
end should restore the proper idle speed - if there's still anything
left of the cylinder bores that is...!