Sounds like the symptoms of a cracked EHA valve to me. When the ambient temperature is cool and the engine cold remove the air cleaner, then start the engine. You should be able to see the EHA valve become wet/moist with leaking gasoline. The leak (at least on my car) is small enough that gasoline won't drip and if you check after the car has run for a while the engine heat will have evaporated any gasoline residue.

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Fred Hoelzle