[W126 Coupe] fast idle, m117.968

[flakeymail-benz at yahoo.com]

howdy,
new member, new (to me) 87 560 sec here.
was looking for any pointers on remedying fast idle -
car won't come down to normal idle speed after start.
this is keeping me from getting emissions
certification (california smog check.)

i'm working with a reputable mechanic backing me up,
but wanted to get any info i could.  he's advising 2
new parts, including a idle control solenoid, that are
looking like $700-$800 (parts).    is there anywhere
else to start on this issue?  any sanity check would
be appreciated.

thanks,
alex

p.s.

some (bad) pictures: 
http://mu.org/~alex/vehicle/vehicle.html