If the engine runs fine at high idle when engine is cold and when fully hot, the engine is going too quickly from high RPM into normal RPM (750). Then is reaching 750 RPM normal idle when the engine in reallity is still cold. You have now two options: either a better adjustment of the fast idle cam will help, or the termo-element is bad and reacts too fast with the coolant temp. You might need to replace the thermo-element. By the way, the correct adjustment of the fast idle cam is done using the coolant temperature of 167°F to 185°F as the reference for the right mark. When the coolant is cold 68°F to 86°F the rod must align with the left mark.
Keep us posted.