View Full Version : Ok, base idle adjustment, can it be done or not?

10-09-2010, 03:19 PM
I have searched the forums and have found a few posts on this. so here is my question, Is there a procedure for setting the base idle on 89SC's or not?

I have had 5.0 Mustangs, 2.3L Turbocoupes and all had a procedure to set the base idle. This involved starting the car with the IAC disconnected and setting the base idle to 400 or 500 RPM. After that, you shut the car off (this is all done after warm up BTW), and cut it back on to verify the base idle setting. Once you reach the base idle, you shut the car off and hook the IAC back up. The computer would then relearn the idle settings and should idle correctly.

Can any verify whether this is true or not? There is a reason why the Throttle body has that adjustment screw on it. Does anyone have a factory Ford manual with this info?



10-09-2010, 07:03 PM

Begin with a cold vehicle. The idea here is to get the car to a firm cold idle with enough airbleed capacity left in the idle circuit for IAC adjustment.

The idle stop should be set first. Back out the idle stop screw, away from the bell crank arm, until about 1/2 turn past the point where it no longer makes contact (blade fully closed). Using an 0.010" feeler guage, tighten until gauge just drags between screw and bell crank arm. Remove feeler gauge. Tighten screw exactly 1 1/2 turns. If the screw is very loose, put a drop of locktite or silicone on it, so it doesn't work out of adjustment.

Now remove the connector to the Idle Air Controller (IAC) just on the other side of the throttle body. Start the car and allow to warm for 2 minutes. Give a small "blip" to let it settle. If it is having a hard time staying running you may have to get an assistant until you can get to the front of the car. Now open or close the air bleed screw (CCW opens) next to the IAC until the car idles at 575 to 600 rpm. For guys with aftermarket cams and an EEC tuner, you might want to idle a bit more briskly, say 650 to 675.

Turn off the car. Now count the number of turns clockwise to close on the idle air bleed screw. If it falls between 1/2 and 2, it's okay, now reverse it out the same number of turns. Log the number somewhere in case you need it for the future. Reconnect the IAC. You are done.

If the air bleed screw is above 2 turns, it's a good idea to tighten the idle stop screw another 1/2 turn, then repeat the idle setting. If it is below 1/2 turn, then loosen the idle stop screw by 1/4 to 1/2 a turn, and repeat the idle setting. Be sure to put another drop of silicone rtv on the stop screw if it was disturbed. Reconnect the IAC. You are done.

10-11-2010, 10:57 PM
i believe the idle is computer controlled so your not gonna change it without a eec tuner or you are way out of range with the idle stop , if the battery was unhooked it may take 2 or 3 days to learn to idle right again