My friend had this problem on his 95 seville sts and I found out the answer. The answer is a technical service bulletin from GM. TSB # 47-60-07

YOUR THROTTLE BODY IS DIRTY AND IT MUST BE CLEANED WITH SOME CARB CLEANER YOU DON'T HAVE TO TAKE IT OFF BUT IT MUST BE CLEANED.THIS IS THE BULLETIN ALMOST EXACTLY SO IT SHOULD HELP.

THE CAUSE IS THE ISC MOTOR RATCHETING IS CAUSED WHEN THE MOTOR IS COMMANDED TO EXTEND BEYOND ITS MECHANICAL LIMIT. WHEN THE TP SENSOR LEARN IS CORRECT (AT MINIMUM AIR, THE THROTTLE LVER RESTS ON THE MINIMUM AIR SCREW) AND THE ISC MAXIMUM EXTEND POSISITION IS PROPERLY ADJUSTED, THE MOTOR WILL NOT BE COMMANDED TO MOVE BEYOND THE MECHANICAL LIMIT.

IDLE CORRECTION:
THE THROTTLE BODY BORE AND BLADE SHOULD BE CLEANED AND RELEARNED USING THE FOLLOWING PROCEDURE:

!!IMPORTANT IF IT IS SUSPECTED THAT THE ISC MAXIMUM EXTEND POSISTION HAD BEEN ADJUSTED WITHOUT CLEANING THE BORE, IT SHOULD BE CHECKED AND READJUSTED IF REQUIRED. CLEANING THE THROTTLE BORE SHOULD BE PERFORMED BEFORE PERFORMING THE IDLE SPEED CONTROL SYSTEM CHECKING PROCEDURE.!!

THROTTLE BODY CLEANING PROCEDUTRE:
1.REMOVE OR DISCONNECT AIR INTAKE DUCT
2.INSPECT THROTTLE BODY BORE AND PLATE FOR DEPOSITS.IT IS NECESSARY TO OPEN THE THROTTLE TO INSPECT ALL THE SURFACES.

3.CLEAN THE THROTTLE BODY BORE AND PLATE USING A CLEAN SHOP TOWEL AND CARB CLEANER THAT DOES NOT HAVE METHYL ETHYL KETONE IN IT (MEK).

4. REPLACE INTAKE DUCT

FOR G-CAR RUN TECH 1 TP SENSOR AND IDLE LEARN PROCEDURE

FOR E,K,OR K SPECIAL:
1. ENTER DIAGNOSTIC;SELECT PCM OVERRIDE PS13
2. PRESS THE COOLER BUTTON
3. KEY "OFF" FOR 30 SECONDS (DO NOT EXIT DIAGOSTICS)
4. PERFORM TP SENSOR / IDLE LEARN PROCEDURE

That service bulletin doesn't really address a "clicking" throttle body. If the ISC motor is properly adjusted it wont click. It clicks as it's trying to reach full extension and the plunger isn't long enough. So the plunger rachets causing the click. The service bulletin is specifically aimed at a dirty throttle body causing a higher than normal extension of the ISC motor. Even with a dirty throttle body the ISC motor will only extend so far before it runs out of travel. If it clicks then it wasn't adjusted correctly. It may have inadvertently fixed a car that was clicking as the clean throttle body didn't demand as much extension of the plunger but the plunger should have been able to extend that far without clicking. Cleaning the throttle body isn't a bad idea, but, it's not a cure-all or necessarily a guaranteed fix for a "clicking throttle body".