1995 z34 erratic idle on cold start only

[Terrski]

I have a 1995 chevy monte carlo 3.4lt that , on the first start up of the day only, has an erratic idle for about 5 to 8 minutes. The rpm will jump from 3500 to 500 and even stall out acouple times. Then the rest of the day it starts and idles just fine. Things I have changed:O2 sensor,IA sensor,MAP sensor,MASS sensor,TP sensor, Fuel pump, fuel filter.Gave up and took it to a shop and the dam car started just fine 2 mornings in a row. He said he did nothing to it. Brought it home started fine for 5 days then went right back to the same erratic idle.Makes no sense. Has anyone out there had or heard of this problem. HELP I am at my wits end with this thing..No present codes set..no engine light on.