My Zetec runs a Focus ECU and very sweet as well......but it takes a few seconds for it to stabilize after revving it even at initial start up its high for a few seconds and then drops to "normal"
is this normal?
will it sort its self out after its learnt the new engine settings?
i have checked for air leaks, there appear to be none.
it has the standard idle valve fitted but not exactly a standard manifold ;-)
not driven it yet (out of my drive that is.....) as i am getting grief from the DVLA.

I found this as well. The ecu will learn and trim it up. You will find it starts hunting a little as it finds the leanest idle it can.


Edit, every time you disconnect the battery this will start again.

[Edited on 5/10/16 by big_wasa]

An idle surge up to 1100 or 1200 rpm is normal but only for less than a second.
After a battery disconnect the ecu has to relearn short term & longterm fuel trims and idle speed stepper motor position.
If you have altered the induction system the factory initial setting for IAC could be out, strange as it may seem having the throttle butterfly setting too closed (ie too slow) is a common cause of high idle speed.
Be 100 percent sure there is no vacuum leak (try the water spray method) and clean the idle control valve and throttle body.