I'm having some very similar issues with my 1994 e420. In the morning, when the engine is stone cold, it cranks immediately. The rest of the day, you have to turn the engine over several seconds before it will start and sometimes it will stumble & die - then crank again and it will start.

Based on the recent comment, I'll check the plug of my 4 wire temp sender. Been chasing this problem for awhile...

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1994 E420