whats wrong with my supra????

[frankwhite]

the other day me and my girlfriend drove my 89 turbo to dinner. driving there it was fine...when we were leaving...i started driving and my engine started missing. i would push on the gas and the car would jolt and not accelerate properly, the rpms werent going up smoothly.the check engine light did not come on...i dont know anything about cars so i took it to my mechanic. he told me a couple spark plugs and spark plug wires were shot and that could be the problem...he changed those and its still missing. he tells me that its just because of bad fuel and i should wait the problem out but i cant accept that. i always fill with premium shell everytime. is it my o2 sensor? fuel pump? please help me!