1999 Saturn SC1 idle air control vavle

Have your car scanned for codes. Several auto parts stores will do this for free. Post the codes here for further assistance.

In the meantime, try cleaning the throttle body. Use throttle body cleaner and a small brush (like an old toothbrush) [don't use a brush with wire bristles]. Often a dirty throttle plates will cause a high idle.

One more thing, are you sure that the new IAC had a O-ring on it. I've seen some techs leave this ring off by accident and it causes crazy idle problems. Also remove the IAC and clean its' port.

Just to add to this one did you take the wire clip off the end of the new iac before installing it?The one the holds the iac plunger in place?Another thing you can try is get some Cardboard and put it over the throttle body while its running. If it doesnt die you have a vacuum leak somewhere. Its very common for the hose from the intake to the pcv in the valve cover to leak. When you install a new iac it should idle real high at first then slowly idle down.