How do you adjust the idle on a 2.5l 87 Chevy Celebrity without screwing up the computer?

Answer 1

Start this project by running the engine until it is at normal operating temperature. Then turn it off and open the hood. The idle stop screw on the model 700 TBI unit is covered by a plastic screw cover. You'll have to poke through it with an awl or something, then pry it off with a screwdriver. The screw is located on the passenger front corner of the unit, so if you're standing in front of the car facing it, it'll be on the bottom left corner of the unit. Then remove the vacuum lines and plug all the vacuum ports on the TBI unit, and be sure to label where each vacuum line goes (a, b, c, etc). At this point, connect a jumper wire from the A terminal to the B terminal on the ALDI connector under the dash. Then turn the key to ON but don't start the engine just yet. Wait 30 seconds, then disconnect the IAC valve electrical connector which is located right next to the adjusting screw. Then remove the jumper wire from the ALDI connector. Now you can start the engine. Adjust the idle screw with the engine running and the transmission in park. Once the correct idle speed has been acheived, turn off the ignition completely and reconnect the electrical connector to the IAC valve, unplug all the vacuum ports and reconnect all the vacuum lines to where they go. Then disconnnect the battery negative cable for 10 seconds and reconnect it to clear out any computer trouble codes. This answer was paraphrased in my own words from the 82-96 Haynes manual for GM A-body cars. I have performed this procedure myself on my own 1989 Celebrity with the 2.5 liter engine and model 700 TBI unit and it does work.