Yep, there's a TSB out on these engines, 3.1 & 3.4, for leaking of a/freeze intake manifold gaskets. I would suspect a faulty OBD coolant sensor. When it was cold, I'd unplug the connector from same sensor and plug into the wire harness, a 10-12K resistor. This would resemble a cold start-up, meaning alittle more fuel and IAC would open up alittle to "fast idle" till warm.
A good way to check out the IAC if working after clean-up, would be to select DEF or A/C, and see if engine rpm remained the same. Check that EGR valve gasket, if not the valve itself for leakage. I would still suspect a faulty coolant sensor or wire harness to the PCM. Coolant sensor should ohm out to 8-12K when cold, 200 ohms or less when operating temp.
Good Luck, yea, spend the money for a diagnostic..........With OBD II, as I understand, memory cannot be cleared until the problem(s) are fixed and the PCM clears itself. I could be mistaken.........
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