probably gas escaping battery/tranny or coolant recovery system

regardless

first thing to do is isolate problem, its most likely ignition or fuel related.
sounds like either your running on 3 cylinders (bad plug wire)
or your fuel filter is needing replacement

try wiggling the spark plug wires with the car parked and idling like you described.

also try smelling the exhaust, if it REEKS of gasoline then you are pushing unburned fuel into the exhaust and its def an ignition problem
otherwise it could be a fuel issue

or of course the other option...compression, either being lost thru the head or somwhere in cylinder (rings)

def sounds like a dead or barely alive cylinder
check it out

~boomer