idle

I have an 89 supra turbo, it idles fine when you just start it and let it run, but when I drive it and take it above about 3 or 4 thousand rpm's and stick in the clutch it drops to about 400 or 500 rpm's and dies unless I keep it in gear. What could this be? Thank You

not quite sure, it might be an alternator but not sure. Try MKIV.com they have a wide selection on Q&A for you. Good luck.

I'm assuming it's sputtering on the way down? First things first, pull the codes and post them up here. Then I can let you know exactly what's wrong if it's anything electronically controlled. Follow the How-to on the online TSRM...
http://www.cygnusx1.net/supra/techtip/engineerrorcodes.html
How is it boosting? At the normal RPM? Still boosting normal PSI? If it's boosting fine and the ISC valve isn't bad then I'm going to say it's the dashpot. The dashpot is the small "vaccume buffer" attached to the throttle body, it slows the throttle plate down so the ISC and engine can catch up when you snap off like your doing. It's very easy to find, it has a small filter on the end of a vaccume hose attached to it. Just snap the throttle a few times with your hand while the car is off and you should be able to watch it work, if it doesn't work (slowing the throttle plate at the last bit of rotation) adjust it till it stops the stalling problem.