[axlrose4eva]

so my 1989 5.0 seems to not wanna idle at sometimes.. the needle on the RPM will be at 1 and then drop down below it and come back up to 1. Sometimes it finds its idle and idles properly.. but then other times it drops below 1 and the engine shuts off. Anyone know what is causing this and how I can fix the problem?

[frozen pony]

hey man i feel your pain haha
you need to clean your IAC and that i think should solve your problem heres a site that will give you a helping hand bud
http://www.moddedmustangs.com/cleaning-your-iac.html
nice stang man, i got a 1990

[90 stock stang]

Check the wires going to your Iac valve and make sure there is a clean connection with no corrosion. I also cleaned all of my grounds including the computer ground and made sure that the connections for the salt and pepper at the top backside of the intake were all tight. Also check for any vaccum leaks.

[EagleAutosports]

Sounds like the IAC to me, either the valve itself or the wiring.
You'll take it off the side of the throttle body, unscrew the two screws that hold the two parts together, and use brake cleaner or carb cleaner on it, and then allow to dry and reassemble and reinstall.