Well, I have first hand experience of a run away. TWICE!!!

The "idle adjustment" cable from a 240D I installed got into a bind while I was moving. I was accelerating from a stoplight, got to speed, let off the pedal and I kept going!!!! I pulled over and basicly did a powerstall from 45 to 0 for 10 seconds. (I did make a nice 6-foot long patch of rubber! ) I then put it in park, released the hood and hit the stop lever. It free revved for about 8 seconds before coming to a stop.

I got everything back in place and it did it again 2 blocks later!!!

After all that, my tranny is screwed! It flares really bad betweed gears and it won't start in 1st now. Pulling the vacuum line halped shifting bat it's still far from right.

Long stoory short: It's not always a problem with the engine that can cause a run away!