1994 Cadillac DeVille 4.9
The Service Engine Soon light went on while I was driving. When I pulled over and did a code search I got a P085. Any recommendations for a fix would be appreciated.

This seems to be a pretty normal problem. Do a search for it there are a lot of posts around here about it.

It means that the throttle body is dirty and the deposits in the throttle bores are restricting air flow at idle to the point that the idle speed control has no more authority to maintain the correct idle speed.

Take the air cleaner off, hold the throttle wide open and look down the throttle bores. Spray the throttle bores with carb cleaner and scrub the bores and backside of the throttle blades with an old toothbrush. Cleaning the deposits off the bores and throttle blade backsides it will restore the idle air flow to the correct level. When the throttle body is clean, disconnect the battery negative cable for 60 seconds to reset the idle learn offsets to the "clean throttle body" default values.

While you are in the throttle body and looking down the bores....see the two tubes sticking up at you from the intake manifold floor just below the throttle blades...??? Those are the EGR tubes and they are NOT supposed to be full of carbon and crud. Rod them out thoroughly with a piece of stiff wire to remove the deposits. Go all the way down thru the tubes to the cast passage below and make sure that they are clean and unrestricted so that the proper amount of EGR can flow.

Thank you Bbobinsky.....Followed your advice and it worked like a charm !

Occasionally I guess and get one right....LOL.

I know this is an old thread but I used this info when my service engine light. I was able to fix it and it improved my gas mileage big time.