what happened to my rx7
 

i was leaving work tonight and my 87 n/a 5 speed did something odd. as i took off i got to about 4000 rpm and after my 3800 stumble my car just took off i had to turn the car off when it hit 8000 rpm, it happened twice has this ever happened to anyone

the throttle cable is probly sticking

A little late, but I just remembered about a similar problem I had:

If it has cruise control, they can fail sometimes. The cc in my 88 GTU failed; if I was cruising and had the cc enabled (but not set), it would randomly give more/less throttle. And if I turned it on, it would just give full throttle and keep accelerating. If you've got cruise, turn it off or unplug it and see if it makes a difference. As for how to fix it, I'd assume that if you resoldered the cruise-control unit, it would fix it; dunno, never tried that. If not, then yeah, check your throttle linkages and stuff.

i have that happen too on cruise control... check the cruise control system