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The idle speed is adjusted with the AIC valve...worst case is that the PO adjusted the idle with the butterfly stop screw and when you cleaned it, the butterfly is held open too far.
The butterfly is supposed to be almost shut, just open enough so it won't stick when you open the butterfly. This has nothing to do with idle...in fact, if it weren't for the aic valve the engine will die.
The closed butterfly also actuates the idle switch on the throttle body...if the screw holds the switch open the ecu thinks you're on the gas and goes to a different point on the map and doesn't control idle speed with the aic. Check for closed circuit on pins one and two (may have to check the wiring diagram for correct pinout) and LISTEN for click when throttle is opened from close. Adjust switch accordingly using two bolts that hold the switch to the tb.
After you get the throttle set correctly on idle, if you have an idle set screw on the bottom of the tb (later cars were electronically set) you have to short to ground a white with blue (green?) tracer wire accessed on the right side of the car, part of a two conductor ending in a socket, just hanging near the amm or slightly back. While this wire is shorted, the ecu is awaiting/memorizing the rpm you set with the big black plastic knob below the tb. Open the wire and the ecu should maintain this new idle speed.
If the above doesn't apply or doesn't work, the next thing is the aic valve...it may just have burnt contacts on the spot where the aic motor has been running for years. If idle is still high, pinch the hose from the aic to the tb and the engine should die...if not, find the vacuum leak or fix the butterfly so it's closed.
Some people have been able to fix the aic motor or clean the shuttle valve...my shuttle valve was ok but the motor was burnt/commutator bars indented so I just bought a new AIC valve about 4 years ago and idle has been stable and 750 in drive since.
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