I also had the same issue on my 1991 Buick LeSabre which turned out to me replacing the magnet. Difficult but I needed to redo the timing set anyways. That cleared the Check Engine Light. Trust me that it really helped but I still notice the bucking! It's not as bad but its still there. I have checked for vacuum leaks. I replaced the fuel filter, put new oil and filter in, and even had my plugs and wires tested. It's still there! Does anyone have any other suggestions?
BTW: I have 229,000 miles and other than that she still runs really well!