Car Accelerates On Its Own problems of the 1998 Mazda 626

Vehicle is very sluggish when accelerating, e. G. From a full stop to 40 mph, esp. In 2nd, 3rd, and 4th gears. Occasionally, the car will "buck" or sputter, then spontaneously catch and accelerate rapidly. On two occasions, I have narrowly avoided collisions as a result of this defect. The problem occurs at least 20 times per day during my 35-mile commute to and from work, yet, when I brought the car to the dealer they reported that they could not replicate the failure. There is occasionally an audible popping sound eminating from the engine compartment on the driver's side just beyond the firewall when the problem occurs. I am afraid that sooner or later my luck will run out. I am aware of a recall covering the pcm unit on the 98 626, but was told by Mazda USA that my vehicle was not covered by this recall. Please advise.