As the temperature heats up here for spring, the car is becoming hotter and hotter in idling conditions. It hovers around 85* when moving but in the time spent at a drive thru, the temp climbs to 100-105*.

Q: Is the Auxiliary fan supposed to come on at 100* whether the air conditioning is on or not? or is it time for a coolant flush?

When the engine temperature increases to these levels, the idle comes down like it should shortly after a cold start. Almost to the point where I have to go under the hood and turn up the idle.

Here's a Scenario:

The car sits all day. Cold, as far as the car is concerned, I start it up and it's instantly at 1500rpm.
Drive around a bit, with my in gear idle speed around 600-900 RPM.
Drive across town (10 minutes) and get in line at a drive thru. In that time, the coolant temp is maybe 60*.
I sit in drive thru for maybe another 10 minutes, and the temp goes up to 100* and I park in a spot. Turn the car off.
If I turn it back on immediately, it'll still idle around 1000-1500. Too fast, but lower than the first start.
If I were to shut it off and let it sit for 10-15 minutes, heat soaks the engine and when I turn the car back on, the gauge reads 115*, and the idle is roughly 520-550 RPM which is perfect and the in-gear idle is about the same.
With this hot engine and nice low idle i begin to drive and as the engine cools back down to 80-85* the idle picks up again and the next in-gear-stop will be 1000RPM.

Q: Could the temperature sensing part of my AAV be shot enough that it only really begins to have an effect at a much higher temp as normal?

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2002 E430 4matic (212,000km)
2002 ML500 'sport'

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