rough idiol seems to smooth out after car warms up
Sounds like a vacuum leak to me. Is the check engine light on? If so, scan for the codes.
May need to clean the Mass Air Flow sensor, use the MAF cleaner only, also would want to clean up the throttle body with some carburetor cleaner, and check the air filter.
Thank You, That would make it a simple fix
Another possibility is an EGR valve stuck open
Yes KenF it would be a possibility but there would be a check engine light on.
I see your post did not come threw there Susan, so do as Tom says and have the vehicle scanned for the trouble codes.
Looking for a Used Century in your area?
CarGurus has 667 nationwide Century listings starting at $2,500.
Search Buick Century Questions
Buick Century Experts