The fast idle on my '90 DeVille 4.5L seems to stay "on" too long, even with ambient temperatures in the 50's. I can't wait for winters here in Iowa! Not!
Also, the off-throttle coast still "sails", although curb idle does occur when the car slows to less than 5 mph.
The high fast idle and the idle "sail" are the reasons I don't drive the car in cold or in icy/snowy conditions. Other than these problems, the car runs beautifully.
Any ideas would be appreciated!
Matt

Sounds like the idle speed control motor (that can on the throttle body with the plunger out of one end that positions the throttle lever) may need replacing.......


Try disconnecting the cruise control link and see if the problem goes away. Possibly it is misadjusted - too tight.

Also, you might just need to clean the throttle body and plates.

Mine has this too. Is it hard to replace it and/or turn off the cruise? I don't use it eitherway...