suction evident on release off fuel cap

ihave a 1999 ford escort when i release fuel cap u can hear suction is this normal as the car does not idle properly

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are you SURE it's suction? Usually pressure!
Does it idle okay with cap off? Though I'm sure you already thought of that...
And thanks for asking specific question about what YOU think it is.. we'll wait for you to DESCRIBE how it idles improperly.
If you want help, that is... otherwise good luck, and dont eat all the fish.
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