i just bought a 1995 z28 with a vortec pro charger and 383 stroker motor and the throttle sticks open when rev'd over 2000 rpm. i went to take it to get smogged and this kept happening not letting it go back to idle so the guy couldnt finish testing it. ive cleaned the throttle body and the throttle cable seems fine. do you know what the problem could be? thanks

 

Do you have cruise control? I could see the throttle sticking open because of that. Also, did you check the return spring? That could have broken or something. Good luck!

 

it does have cruise control but i dont think it works ive tried using it while driving it but nothing happens. dumb question but wheres the return spring?
if not what else do you think could be the problem?

 

What brand throttle body?

The throttle body return spring is on the quadrant on the driver's side of the TB, coiled around the shaft.

Is it possible the pressure of the boost over 2000 RPM is holding it open, or causing it to be hard to rotate?

 

i was going to suggest that, but then decided it would sound silly. unless the return spring is very very weak, i dont think it would ever happen. however, cruise control doesnt have to work to cause problems. at least on my 02, when you press the gas with cruise control disengaged, the plastic piece that connects the cruise control cable to the throttle body slides over the cruise control cable. it could then possibly stick.

 

Is it nice and smooth without the engine running?, always goes back to closed throttle when not running?. To eliminate the cruse control just un clip the connector from the throttle body, it just pops on and off (not the whole cable from the mount as its used to lock the throttle cable in place)

 

Snap the throttle closed on a high boost setup, and I've seen the shaft on a monoblade bend. The blowoff valve action is not instantaneous.

If there is any corrosion or dirt in the shaft bearing surfaces, it isn't going to take much at all to make it difficult to turn. Some of the aftermarket TB's have problems with the return spring, even without boost.