I tried all sorts of things when my 86 420SEL did the same thing...after spending a fortune at the dealer and throwing parts at it, I broke down and put new spark plugs on it, and lo and behold, found a corroded spark plug wire that was apparently intermittently cutting spark to one cylinder. At low RPM that was enough to make it stall. It runs like a top now, 1 year later.

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2002 Ford ZX2
2 x 2013 Honda Civics