Mika, the EHA valve on our 1991 300CE developed a hairline crack which leaked gasoline and caused a strong gasoline smell under the hood. I suggest removing the air cleaner housing to expose the EHA valve then start the engine and closely inspect the EHA valve for evidence of leakage ... the black plastic will get wet, but probably not drip so you have to look very closely and/or wipe it with a paper towel. Replacing the two green O-rings did not solve my problem. Needed a new EHA valve.

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Fred Hoelzle