Hi there - I have a 1999 Mazda 626 with about 100K. Haven't had any problems, until yesterday when I went to pass someone from about 5 mph, I heard a 'pop' and then from that point on, there is random times of hesitation and rough acceleration, like it's not getting going... it stays for a second or two, the car accelerates, but with less power, and then it catches up and is fine. Seems to shift gears fine and all that as well... Other than that, no issues at all...

Any ideas? Fuel filter? Maybe I blew a spark plug or something? I know nothing, and my mechanic isn't open til Monday.
Help! Thanks in advance!