Well I'm here to argue with you sir. I'm trying to help!
I Know What a 3.1 V6 is! I'm just telling you what I have in front of me.
The Diagram I sent you is for a 1996 Oldmobile Cutlass Supreme with a 3.1 V6.
If your vehicle has a Mass Airflow Sensor then I'm looking at the wrong one. Can you give me the 8th V.I.N. digit and I'll try to find the correct diagram for you.
As for helping you so far... I HAVE answered your question as to what can cause this...
If it worked before and all you did was change t-stat and the Coolant Temp. Sensor
then it didn't work as you'd expect, You have got to have a faulty sensor! If you have 35 Years as a tech then you must know... What else could it be?
If you get me the 8th digit I can get you a diagram.
I found this diagram for a late 96-97 model...
If you look at the coolant temp sensor it still has the yellow and the black wires but has a dark green wire for a cluster feed.
I'm trying to help!