My W126 420SEL is doing the same thing...the recirc button on the HVAC panel clicks in time with the stalling/stumbling. I have been trying to locate the problem, and when I unplugged the OPV box the idle climbed several hundred RPM's and the stumble went away for the moment anyway. Mine doesn't die, it just stumbles under load.

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2002 Ford ZX2
2 x 2013 Honda Civics