Originally Posted by LinuxGuy

I just posted this in another thread, and thought I would make a seperate thread containing the same info since it might come in handy to some other folks.

This idle adjustment procedure worked great on both of my 2.8L Camaros to get the idle back to normal. (Especially the my 89 5-speed that was stalling at stops. The throttle plate was not even close to being open enough at idle.)

I have done the adjustment twice on the 2.8L V6 (once for each of my Camaros), and I can say the adjustment worked well in both cases. As for the 3.1L V6 adjustment, I've never had a 3.1L to adjust the idle on.

Note that there is an IAC and TPS adjustment tech article at thirdgen.org, but this article is not as specific and does not specify the RPM settings for the V6 engines (only the V8s). For a version of this instruction list for V8s, see this thread: https://www.thirdgen.org/techbb2/sho...hreadid=214817

Taken from the Chilton's Chevrolet Camaro 1982-92 Repair Manual.
My own comments are added in italics.

Before you do any of these adjustments, make sure your timing is where you want it. I have found that changing timing will subtely affect the idle.

Multi-Port Injection (MPFI)
2.8L Engine
1.) Using an awl or equivalent, pierce the idle stop plug and remove it. This is the plug covering the idle speed adjustment screw (aka idle stop screw, aka minimum air adjustment screw) on the back side of the throttle body.
2.) Leave the Idle Air Control motor connected and ground the ALDL diagnostic terminal (connect a wire between the A & B terminals on the ALDL connector). Turn the ignition to the ON position, but do not start the engine.
3.) Wait 30 seconds, and with the ignition switch still in the ON position, disconnect the Idle Air Control connector. (Since the A & B terminals are connected on the ALDL, the ECM will place the Idle Air Control Valve in the park position. Disconnecting the IAC connector will keep the IAC at this setting.)
4.) Turn the ignition switch OFF. Disconnect the distributor set-timing connector. (i.e. - The wire on the firewall you disconnect before adjusting timing.)
5.) Remove the ground wire from the ALDL connector. Starting the engine with this jumper wire in place may damage the ECM. See more info from "Vader" here: https://www.thirdgen.org/techbb2/sho...hreadid=211733
6.) Start the engine, then connect the A & B terminals on the ALDL again. This will place the ECM in Field Service Diagnostics mode which will flash the SES light according to open/closed loop status. Allow the engine to reach operating temperature and go into closed-loop operation. Watch the Service Engine Soon light on the dash. When the light is flashing 2-3 times per second (i.e. - rapidly), the engine is in open-loop mode. When the light is flashing about once every second (i.e. - slowly), the engine is in closed-loop mode. Once the engine is in closed-loop mode, continue to step 7.
7.) Adjust the idle stop screw to 500RPM in D if equipped with an automatic transmission or 600RPM in neutral if equipped with a manual transmission.
8.) Turn the ignition OFF and reconnect the Idle Air Control connector and and the distributor set-timing connector. Remove the A & B jumper wire from the ALDL connector.
9.) Adjust the throttle position sensor to 0.54v at closed throttle since adjusting the idle screw has changed the position for closed throttle. Start the engine and check for proper idle operation. You will have to disconnect the battery to clear the code set from disconnecting the distributor set timing connector.

3.1L Engine
1.) Disconnect the negative battery cable. Using an awl or equivalent, pierce the idle stop plug and remove it. This is the plug covering the idle speed adjustment screw (aka idle stop screw, aka minimum air adjustment screw) on the back side of the throttle body.
2.) Ensure the throttle or cruise control cables are not holding the throttle lever from returning fully. Back the throttle stop screw out until and air gap is visible between the screw and the throttle lever.
3.) Turn the screw in until is just contacts the throttle lever; then turn the screw in an additional 1 1/2 turns.
4.) Connect the negative battery cable and connect a suitable scanner to the ALDL connector to monitor the Idle Air Control (IAC) valve counts.
5.) Place the transmission in P if equipped with an automatic transmission or neutral if equipped with a manual transmission.
6.) Start the engine and allow it to reach normal operating temperature and enter closed-loop operation.
7.) Monitor the IAC valve counts with all accessories OFF, the IAC reading should be 10-20 counts. If not as specified, repeat the procedure.

Edit - 9/6/2004:
Changed idle RPM numbers for 2.8L engines to 500 and 600 RPM from 550 and 650 RPM (these are the numbers found in the GM service manuals).
Added step instructing removal of jumper between ALDL A & B terminals before starting engine (due to possible ECM damage). Added step instructing the connecting of A & B terminals after engine is running to place the ECM in Field Service Diag. mode.

Originally Posted by drdave88

coming from a mechanics POV, if its idling too high, theres something wrong. that plug should not ever have to be removed to adjust idle. it came from the factory idling normally and should never be removed. thats the easy way out to band-aid your problem. and doing that may not even help you pass smog. you may have a vacuum leak causing it. you may bring your idle down, but you wont help the leak, causing a lean condition. just as an example. so id say not to do that. find out why it idles high and fix it right.

Originally Posted by drdave88

wow, honestly, i expected to be slammed for that post, lol.

Originally Posted by mightyfbird88

Wouldn't a vacuum leak cause it to idle irratically, or not necessarily, because my idle is pretty constant, its just high

Originally Posted by darkangel777

How do you tell if the iac motor is shot?
Also where is the idle adjustment screw?
Sorry for the newb post.