I have heard from a number of Z owners about their throttle sticking in really hairy situations.  And in deed it happened to me last March.  I was approaching an intersection in the left lane and wanted to be in the right lane to make a turn. The intersection was coming up fast so I hard accelerated to pass a car to my right.  When I backed off of the peddle the car kept accelerating!  Quickly I pushed in the clutch and hit the brakes. The engine was revving like mad so I shut off the ignition and rolled around the turn. 

What I found is what I would consider a minor design flaw in the throttle assembly which could have grave consequences. At the exit of the throttle cable guide is a rubber boot intended to keep out dust and water while flexing with the cable.  But after a decade the rubber dry rots and becomes brittle. In these cases the boot breaks off and slides around on the cable.  It could remain this way for weeks, months even years.  Until, under just the right combination of acceleration, braking, bouncing, turning, and maybe timing and luck, the boot slips forward enough to wrap around the throttle half pulley with the cable.  The cable can't drop between the guides of the half pulley and instead rides on top holding the throttle open to 3000 or 4000 rpm.  The fix is easy.  Rip that sucker off of there and it doesn't happen again.

TERUG NAAR TECHNIEK