Check for low fuel pump pressure or filter blockage, does it happen while accelerating or going up hill under higher fuel demand? It would then run normal if you back off the throttle, getting proper fuel volume. Otherwise Spark/coil/carbon arc cutout if there is some backfire. listen for carbon arcs, watch the wires and distributor in darkness for any arcing. It leaves tracks sometimes inside the distr cap or on the rotor. I have seen rotors with signs of sparking off the back side and down through the center shaft. A blocked catalytic converter has a hissing muffled exhaust sound.