87GT - are your throttle body and iab solenoid completely clean and free of build up? If it won't idle properly or low enough, it's often because the iab solenoid has built up oily sludge in it over the years -- part of the pcv design produces this side effect. If it's clean and functioning correctly, the idle ought to come down to the factory setting of around 675. If you've got a factory tach, they're notoriously inaccurate. If that's what's reading 850 - it could simply be off. Use a calibrated shop tach to check it. Lastly, don't set the tps above .95V. The system thinks it's not idling if it sees above 1V, and getting that close seems to throw some of them off. Jerry's right - .85V-.95V is fine. Lastly, are you sure the throttle stop is set correctly? Back the screw out away from the throttle linkage, insert a .003" feeler blade and tighten the stop until it just touches the feeler. Then remove the blade and tighten the stop another 1/4 turn. That puts the blade at the factory setting. TPS should be set engine warm, not running, ignition on. And disconnect the battery after all that to clear things out. Give it some time - it may search around a bit as you drive it for a day or two.
