Ford Repair: Idleing, vacuum leak, air vacuum

Question
I have a 1990 Ford Taurus 308 Engine.  The engine races at variable speeds and sometimes surges at idle.  A vaccum leak has not been found when a smoke test was done.  The EGR, IAC, air temp sensor & brain (this fixed the problem for one day) have all been replaced.  The air intake box also whines at high idle.  Sometimes the cruise control acts funny.  This crusie control problem started at the same time as the idle problem.
Thanks!

Answer
Engine racing is usually caused by unmetered air (vacuum leak).  Also, some cruise control servos are vacuum actuated, which would explain the link between the two problems.

I don't know of anything that would cause an air box to whine.  I would check the air box mount, hose clamps, and intake tube for holes or splits.  

The best way to check for a vacuum leak is to spray carb cleaner on a cold, running engine.  The idle will decrease and turn rough as the carb cleaner is ingested, if there is a leak.  

Hope this helps,

Dave