I dont think it has a canister evap or purge valve. you see it on newer cars that had to meet stricter emission standards. It has the cis fuel injection. I get hissing when i open the fuel cap on any gas car. you are releasing the pressure in the tank. Whenever you do a fuel system service on a car you remove the gas cap so the pressure in the tank doesnt bulge the tank

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)