Ok, it sounds like one cylinder is not igniting properly. If the pfft pfft
sound is pretty regular like it's the same cylinder, then it must be
ignition or fuel injector to that cylinder. Pull each spark plug wire and
note the wire that does not change the misfire characteristic. That's the
one you need to completely diagnose. Pull the spark plug, check resistance
to that wire, check the distributor cap for cracks, contact points for pits,
any moisture inside of dist cap and any dirt particles in the Crank Angle
Sensor disk inside the distributor. If there's any moisture in the dist
cap, replace it and the rotor cap. (Both my Max's had cracks in the dist
caps which allowed moisture in. They were REALLY old, but your's still could
have a defect, so check them anyway.)
Also, check the fuel injector wires to make sure there are no cracked or
loose connections to the fuel injectors. That would definitely cause a
regular misfire. Did you wash your engine compartment or did it rain last
night? Water and moisture
can cause a short in the ignition by allowing the spark to jump to ground,
and moisture in the dist cap will also cause a short.


Chris
90 & 94 GXE's