Need help with high idle. (e38 conversion)

I am working on an engine conversion in a 1983 Ferrari Mondial. The donor engine is an LZE 3.5L flex fuel from a 2009 Impala (e38 ECM) with a Porsche standard transaxle. The 4T65E and TCM from the donor Impala were not utilized. The car is running and driving now with no problems other than a graduall very high idle. When you initially start the engine at around 75*F ambient, it will idle around 900RPM and gradually work its way up to 1200RPM and eventually up to 1800-2000RPM. Here's the tun file and I'll be happy to log any PIDs needed. The only PID that catches my eye is VSS which is pegged at 158MPH, a side affect of a missing TCM I imagine. Anyone know how I can isolate the table(s) that are causing this high idle? Thanks- Brint.Attachment 16949

I finally have this issue resolved. A very helpful member here has spent a lot of time helping me via PM. Thanks you very much!!!

We tried to solve this problem in the tune but ultimately had to install and wire the TCM into the CAN bus in order to get the VSS pid to display 0 mph sitting still. This seems to have cured the high idle situation. It's still hard to believe I have to run a TCM just so the ECM will follow idle commands but I guess I have an oddball conversion here.

Anyways, thanks for all your help sir!!

Good job, and thanks to whomever helped :cheers: