So, whenever I start my car after say 4 hour of sitting it will start up with a bit of a longer crank usually 3 seconds and it will sound like it is running rough but not backfiring. it sounds more like it is missing and the rpm's show this as they run smooth then drop durring the miss sound and then go normal and this goes on for about 15 minutes in idle. however if I put it in drive right away it still sounds slightly rough but seems to be running better and when the engine is warm near operating temperature it runs smooth as hell at 600rpm and needle does not even move one bit. Took it to a few mechanics and none seem to know exactly what is causing it but all say the iac or aic, can't remember right now, might be going bad causing this.

my truck is a 2001 dodge ram 1500 sport 5.2 magnum auto.
it currently is showing 2 codes one a small evap leak the other a large evap leak.

I think the codes are caused by my rotted gas neck tube, though and the truck ran pretty smooth ( if im remembering right ) before that.

also is the 600rpm the right idle speed? My engine was swapped recently but before that it idled around 750 rpm.