Check out the MAF. My 280Z had the same exact problem. After 600 bucks for fuel injector rewiring, spark plugs, wires ,troubleshooting, and tuning.
I took it home only a little better off than it was. I ordered a new MAF. I plugged it in and still no improvement. then I found a wire that was connected directly to the body. I unplugged it and BAM! instant fix. for whatever reason that wire was grounding out the MAF and it apparently screwed up the old one. also, I found that the unit was grounding out in the rain too. the water would find its way up into the engine bay and build up between the metal plate holding the MAF and the MAF itself causing instant bucking and finally, loss of power. (I neglected to put the splash shield back after some work) not sure how similar my 75 280z and you car are, my Z has a straight six, and is Fuel injected. Well there is my advise. Hope it helps.