Idle Stop

Yes I know... Idle stop usually doesn't need adjusting and is seal on many engines.

Warning: Do not use a ECM Scan tool to make this adjustment! ECM scanner mess with timing and gives you higher RPM.

Notes:
Use a good tachometer, not the dash tach. It is easer and more accurate.
Once you are done, clear any errors that may have been set in the ECM.

300 TBI, 1984-86 L4 Fiero

You need a special tool, GM Tool J-33047, to plug the Idle Air passage.

Plug vacuum port on TBI unit for Thermac.
Connect a tach to engine
Start engine, Auto trans in Park (Man trans in Neutral), and allow engine RPM to stabilize.
Install tool J-33047 in idle air passage of throttle body. Be certain that tool is sealed and no air gets thru. (See image below.)
Using Torx #20, turn throttle stop until:

Auto trans, 500 +/-25 RPM

Man trans, 775 +/-25 RPM

Stop engine and remove the tool from TBI unit.

Source: 1986 Fiero Service Manual, page 6E2-C2-8.

700 TBI, 1987-88 L4 Fiero

Plug any vacuum port, as required.
Jumper ALDL terminals A & B.
Turn on key, engine off, and wait 45 seconds. This will close IAC pintle.
Unplug IAC while key is still on.
Turn key off and remove the ALDL jumper.
Start car and set Idle Stop screw for 600 +/-50 RPM. (550 - 650 RPM is fine.)
Shut off the car and plug the IAC in.
Replug any vacuum ports.

Source: 1988 Fiero Service Manual, page 6E2-C2-12 thru 13.

Port Injection, 1985-88 V6 Fiero

Plug any vacuum port, as required.
Jumper ALDL terminals A & B.
Turn on key, engine off, and wait 20 seconds. This will close IAC pintle.
Unplug IAC while key is still on.
Turn key off and remove the ALDL jumper.
Start car and set Idle Stop screw for 800 +/-50 RPM. (750 - 850 RPM is fine.)
Shut off the car and plug the IAC in.
Replug any vacuum ports.

Source: Based on 1986 Fiero Service Manual, page 6E3-A-56 item 3.