355 idle question

Thanks for reading.

My 355 feels a little bit shaky when idle, although the idle indicator on dashboard looks stable (no ups and downs... it satys above 10rpm). It may not be a problem at all and probably the 355s are all the same, but I hear an air-flow-interrupted kind of sound, therefor the care shakes a bit. Spark plugs and wires were replaced and it didn´t fix it,

Anyone´s input on what to look for, or where to look, is greatly appreciated.

No check engine light on either by the way.