Strange engine rev at cold start

At cold start my revs are behaving strange at start up. Usually I just get in and go, and have noticed a hesitation but not a stall. 
Not sure if it relates to this:  www.bigjimny.com/index.php/forum/7-jimny...evs-service-bulletin

The other day I just stretched in and started the engine without touching the throttle. engine revved up to its usual 1200ish rpm before after 5 sec it wnet down to 5-600 or so for a few seconds, before the rev went up to 1800rpm. Didn't sound like it was running even so touched the throttle for a blink and then it got stable at it's usual 1200. runs great otherwise and this happens intermittently but might be more otfen when the temp is at zero or below.

Have anyone seen this or have any idea what it might be?

Is there a temp sensor that makes the rev increase on cold temperature? 

Edit: Car is 2005 VVT with all the m13a stuff on it but a m16 VVT engine block.