I've had a throttle stick open on me twice, and it certainly gets your attention. On my 911, it was because the throttle and clutch cables were twisted (I had recently replaced the clutch cable) and the clevis on the clutch cable was hitting something. On my SE-R, I had left the positive battery terminal cover on top of the engine by accident and it bounced its way into the throttle mechanism. Oops!

I shifted to neutral, car bounced off the rev limiter twice, turned off the engine and coasted to the shoulder. all in a matter of 5-10 seconds.
thank god I was able to do that. the right lane was actually busy too. can't imagine what i would do if there was no shoulder..

I tend to agree. I would trim back the metal on the bulkhead area, and rebuild the cluster on any early 911.

I realize this is an old post recently brought up again but I will post this for future reference.
If the bushings are ok another cause of this can be the little arm getting bent. this is caused by the gas pedal not reaching the gas pedal stop before the throttle rod hits the throttle stop at the intake. As you mash the throttle the top of the throttle arm bends because the middle cant travel any further as it is restricted at the mid-point by the throttle rod.
Get someone to watch the throttle stop while you fully press the gas pedal. the throttle should not actually hit the stop. This is a pretty easy check every one can do to prevent a pretty scary and dangerous event.

IIRC the pedal board has the stop so if you were driving without it that also could have contributed to torquing the arm.