Other things you can look at for this are:
- Check all vacuum lines, check there is no leak. As import non turbo supra use the map system, they compensate for leaks by increasing idle speed.
- All na supra's have a cold start where they rev up high to 1500-2000rpm until engine is warm, make sure it isn't this
- Check your ignition timing is set at 10 BTDC
- I have noticed that the non turbo throttle bodies can suffer from a sticky throttle if they are high mileage. You can see if this is happening by pressing the stop on the throttle body that sits below the adjuster till it goes back down. If the revs drop, then this is part of the issue. You can try cleaning out the throttle body/iacv but if it makes no difference then I'd get another second hand TB, I had to do this to mine before it started idle'ing @ 800-900
- If you are really handy with mechanics, then also check your TPS sensor position outlined in the Supra repair manual. I wouldn't bother touching this unless you have the right tools however.