I`ve had a idle problem that is constantly annoyed me for months at this point. Cant seem to figure out what the problem is. Rpm is high at start up/cold start at 2000 and then slowly going down to about 650 which is good at first glance, then it proceeds to drop to 300rpm and almost stalling in the process. This drop is short and it quickly stabilizes back to 650 for about 3 minutes and then drops again. I`ve heard something about the ac changing the rpms which is not the case for me.
My Z has almost 124k miles
Background info:
-Checked for vacuum leaks, none found
-Cleaned TB (this did nothing for the idle and was the same as before)
-Cleaned maf same story as the throttlebodies
-Changed sparkplugs to oem spark plugs
-Done the throttle body relearn and the idle relearn
-Changed the seals on the upper half of the plenum
-Pcv replaced
-Replaced camshafts/exhaustshaft position sensors on both banks
-Replaced crankshaft position sensor

I have aftermarket intakes and also a militek catback exhaust. What i have been able to find out through the forums is that this can be a ecu issue? Would like to hear some more tips before i go ahead and change my ecu.
Grateful for all tips!