[V8] rough start-up idle

[Scott Simmons]

Car cranks fine, starts up to about 800-1000rpm, then drops down to a 
very low number, the first mark on the tach (200?) then back up and 
holds 600-700 as a stable idle.  Only does this on the start-up, no 
trouble when getting off throttle or idling at a stoplight.  Just 
starting (and usually just the first start).  When it dips down to 200, 
my lights dim (naturally), but car picks itself back up and holds the 
correct idle.

Aging ISV?  Any other ideas?

~Scott Simmons