91 200 hesitation

[RRFS32D@prodigy.com (MR JERRY BEER)]

Car has developed early morning sickness.  Car starts fines and 
idles/runs fine for about 30 seconds.  Then car develops a hesitation.
 If left idling, the idles speed hunts between 800 and 1000 or so 
rpms.This will last from 1 to 2 minutes and then clears up as the car 
warms up.  After that car runs fine. I thought O2, but then the car 
should not run well after warm-up.. Is there something in the warm up 
circuit to look for?  All replies welcome. TIA.
Regards, Jerry 91 200tqw
South F.L.A.