Just listen and feel around for the vacuum leak or as Jarrad suggests you can try spraying any suspect areas while it's running and see if there's a difference in engine pitch.

I suspect your aux air valve is working, as the revs are dropping back as they should. Normally they make the car idle fast until warm.

Perhaps your 5th injector isn't getting power. There should be 12v at the injector when the engine is cold. It's controlled by the thermotime switch on the head water outlet.

Another problem I've had is the idle speed adjustment screw in the throttle body working loose. This leads to the idle speed adjusting itself. This fix for this is easy. You just replace the o ring on the screw shaft. I used one from a multi pack of o rings I got from Bunnings for 99 cents.

Pete