Classic/Antique Car Repair: High Idle speed, vacuum leak, vacuum lines

Question
QUESTION: My 1991 Ford Mustang LX, 4 Cylinder idles at 1100 to 1300 RPM when in park and neutral.  When put into gear with brakes applied the idle is around 750.  This problem all of a sudden started.  The only problem I could find was a bad PCV valve.  After changing that it did not change the idle.  All vacuum lines are good to go.  What could be caused this problem?

ANSWER: what is the problem, the high idle or the low? this sounds fairly normal for an engine that size.


---------- FOLLOW-UP ----------

QUESTION: The High Idle

Answer
There is a step linkage on the carb that is for the choke to keep the idle up at first. Sounds like it is not returning to its proper position. Could be binding up or need cleaning with carb cleaner on the outside.


Also, check for a vacuum leak, it can cause high idle.