It never actually stalls, or hints at stalling... just a random misfire, that gets worse the hotter the engine gets.
It shakes the car.
I have listened to both of the fuel pumps at idle when it does this and there is no change in pitch that I would expect based on a faulty pump relay issue... but maybe I am wrong.
I agree based on logic that if the crank position sensor was missing signals that could be the culprit, but its odd that it seems directly linked to underhood temp. I suspect a componant in the engine bay, but I might be wrong!
If you drive the car at speed on the freeway and then stop its fine, or only does it a bit... only in slow conditions/ and with the A/C on does it get worse.
When its at its worse, its like a couple/3 of plugs leads are off... but its not consistant like that sounds. Its sounds really random, when its cold it runs perfect.

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2009 Mercedes ML320 Bluetec

Well, we replaced the coil with a used one just to try to narrow down the search... made no difference.
I tried to replicate the misfire by pulling the plug leads off to see if the misfire stayed the same .... It was really noticable when each HT plug was removed...
I plan to do a compression a test next and to check the resistance in the plug leads when hot...

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2009 Mercedes ML320 Bluetec

See post #5:

300E Apparent Misfiring, Hesitation

Just one more thing to check...

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

We found out that the engine needs valve oil seals.
See this thread:
Spark Plug Horror! Look!

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2009 Mercedes ML320 Bluetec