I think this may have something to do with the Air Cond. system. Ever since I have had the car, the clutch on the compressor has always been engaged. It does not matter where the switch or lever settings are on the console. Someone in the past may have altered the wiring.
Your indication that the RPM should drop to 800 when the temp reaches 150 degrees is about what it is doing. It takes about 4 minutes to get there with a air temp. of around 80 degrees (car sitting). Does this sound too long??
I have already checked the cold start system and it seems ok. The two temp sensors should be ok, I relplaced the coolant temp sensor and the resistance readings of the air horn sensor are correct and it slightly changes the rpm when the wires are removed. The vac. relay does work, if you pull the plug while cold, the rpm will drop and you hear the relay click. Put the plug back in and the car races back to higher rpm as it blocks the vacuum.
I thought my next step would be to take the Aux. Air valve off and clean it.
What would be the best way to defeat the Air Cond. engagement system to see if that is the culprit?
Thanks for the help, again