Monitor your Idle Control Valve voltage. I suspect the valve is gummed up and not responding well until engine heat loosens the internal lubricant. If, however, voltage to the valve is low or null during warmup, the problem is elsewhere. If it is the valve, clean it or replace it.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7