Hmm, re-reading this. realised you said it wasn't revving up and coming back down, it was staying there up at redline, and starting engine it idles, albeit high and as soon as the throttle is pressed it revs off the scale.
defo check out your throttle body out for a sticking mechanism. Best best would be remove your throttle body, good strip and clean, replace TB/manifold gasket.
Have you had a chance to look around the throttle body yet?