Hey, Neil! Haven't heard from a fellow Canadian in a while!
Here's a few possibilities:
-Slight vacuum leak or unmetered air between the throttle body and MAF.
-Dirty, possibly low flowing injectors
-Dirty or sticking IAC
-Dirty or faulty MAF sensing tip
The fact that this only happens during a very short period after cold startup would seem to indicate an air/fuel mixture problem; while the PCM is in Open Loop, it does not read O2s (among other things) and makes no attempt to correct A/F mix.
Once the O2s come on-line and the PCM goes Closed Loop, it sees the A/F discrepancy, makes a fuel trim correction, and the rolling idle is gone.
Look for any cracked, damaged or disconnected lines or tubes. Remember, if it's an air leak, it won't be very big, because if it is, and the PCM has to make more than a 10% long-term fuel trim, it would set codes and trigger the MIL (check engine light).
Re'n're your MAF and spray the sensing tip liberally with Tune-up or Carb cleaner. Not just a couple of psst-pssts; hose it down with about half the can! Don't touch the tip, don't wipe it down. After re-installing it, let it dry completely before firing up the car.
If your injectors are restricted enough to cause Open Loop A/F problems, dumping some type of cleaner in the tank may not help. Go to a shop that can give you a proper high pressure injector flush, done through the Schraeder valve on your fuel rail. At 190,000 kms, you're long overdue anyway.
If your problem is the IAC, it should occur both hot and cold, but I've seen them do some strange things. If you haven't done it in a long while, re'n're and clean that with Tune-up or Carb Cleaner.
Let us all know what you find.
